The need for concepts like words and phrases are primarily designed the needs of our particular communication system using sounds or written words. Those limitations are tossed away when we free ourselves from the medium. Take, for example, the amount which can be expressed by a single touch. The poets have oft drempt of the raging warrior subdued by a single touch of the gentle soul who loved him.
Touch itself is limited compared to what an Ent crown can do. Needless to say the Entish crown's description suggests an even tighter connection between the wearer and the ents than a pair of lovers would dream for. The scientist in me wants to suggest direct neural stimulation, but it probably doesn't even need an explanation. Just a sense -- a feeling.
If I may borrow from Douglas Hofstadter's way of viewing the world from I am a Strange Loop, I would suggest they may talk in "symbols." A symbol conveys one thought or idea, but unlike a word or phrase, there's no concept of ganging them together. A symbol is a complete thought, not to be divided or aggregated. It is not unreasonable to presume that the answer to "What is the sound of one hand clapping?" is a symbol when approached from a Zen perspective -- indivisible, fleeting, and yet eternal.
Without the ability to combine symbols together, an Ent (or indeed perhaps all of Ent kind) cannot transition from thought to thought by simply switching from symbol to symbol. Instead, they must mold and manipulate their one symbol to include the new idea, and then perhaps elect to manipulate it to exclude the old one (though we may have reason to believe that the old idea always still exists in the form of a whisper). With an Entish crown, we are permitted to experience this symbol as part of the Ent community.
In the original wording of the question, there was a reference to Julia fractals. I do not think that wording was amiss, and I would like to include a little piece of that. Such symbols could be thought of as self-similar. The whole pattern of the symbol could be rediscovered within any silver of the symbol, as fractals often exhibit self similarity as you zoom in. The symbol may be distorted, depending on how one approached that silver, but it would always be there. The closer to the center of the symbol one looks (or feels), the less distorted it is -- the more the true meaning of the Ents shows through.
If you were to put on an Ent crown, you would be permitted to join the Ent community, momentarily, and see the Symbol of the Ents from far far away (the less like an Ent you are, the further away you would feel). Even at this initial distance, you would feel the pulse of the spirit of the Ents, though it may be very faint.
From that point, you interact with the Symbol as the Ents do. If you wish to go closer to them, you manipulate it to include more of yourself. That act naturally shifts your focus closer to the core of the Symbol -- thinking more and more like an Ent. You would not ask them a question and then await the answer. You would ask your question and the mere act of asking would lead you to the answer, as though it had always been there.
This sort of communication would lead to the appearance of communicating with hallucinations. Any individual wearing an Entish crown would be forced to describe their journey in that way, as the Ent's spirit literally applies itself over the hopes and memories of the wearer, making them part of the greater Ent while sharing some of what it means to be an Ent with those hopes and memories. To go beyond calling them hallucinations would imply your mind had been warped enough by the Ents that you were indeed no longer a human, but an Ent yourself. In such cases, you may not survive having the crown removed from your head any more than one survives having their head removed from their shoulders.
Alice picked up the crown of RedAlder and looked up at its namesake. RedAlder stood taller than any other tree in the region, its maturity shown in its warped yet beautiful branches suggesting a subtle harmony that only an Ent could accomplish. He was by far the easiest of the Ents to talk to, having served as ambassador to this kingdom for far longer than anyone alive could vouch for personally. Nevertheless, she hesitated. She knew that you never walk away from a conversation with the Ents the same. Some part of you is always changed. She took a deep breath, closed her eyes, and allowed the crown onto her head.
Even when talking to one as soft and kind as RedAdler, the experience was never easy. She could feel RedAlder guiding her to a soft calm space within the Ents carefully pruned and cared for, as though they were their own arborist. She could feel herself arrive, as the impossibly bright lights and twisted sounds faded away and gave her a moment to rest... if the idea of a "moment" meant anything at all when connected to the Ents.
Drawing upon the lessons she had received from RedAdler and the other Ents, she carefully drew her awareness to the ebbing and flowing around her. She soon found what was thought to be the Pulse of the Ents and began her true quest. She focused on developing her own symbol within the Symbol, to add her own tale to the Ent kind. RedAdler kindly assisted the entire way, helping her manage her emotions while she struggled with the delicate grammar of the Symbol. After some time (time?) it was completed, and her story of the upcoming war was offered as a gift to the Ent spirit. She felt it race along the Pulse, deeper into the Ent kind. Surely they would appreciate the fires that were to come to their forest and lend aid.
Something was wrong. She felt no reply, even though her statement had been given. The replies were always instant -- infuriatingly instant, as though the Ents never had to spend any time on their decisions (there's that word again, time...). She had no training to help her now. None of her teachers had ever suggested this could happen. She struggled through her intuition to find an answer (her? Pronouns were so hard when talking to the Ents. Maybe it was "our intuition?" ... "my intuition?")
She widened her awareness, and realized how distant she felt from the Ents. Perhaps they had given her answer and she simply had not been listening. She felt for the pulse, and upon finding it, began weaving her own symbols closer and closer to it.
RedAdler interceded, in a flurry of symbology that would have sent Alice into a disoriented spiral if she had not been so focused on feeling the pulse of the Ents. He caught her, and directed her, guiding her weaving to take her closer and closer to the pulse. But when she got there -- wait. She got there? One never "gets" to anything with the Ents unless its just a carefully cultivated landing pad managed by their ambassadors to humankind. But there she was, on the pulse -- part of the pulse. Her entire essence shook with every quiver of the Pulse around her. RedAdler was there (how long was he there? This time thing again... how infuriating!). The Symbol looked different to her than it had every looked before. It was more nuanced and detailed. Alice could almost feel the entwined roots of the Ents, sharing in a way no two humans could ever achieve. She saw the Pulse in a whole new light. Two lights. Three lights. Five? The Pulse raced everywhere around her, until it dawned on her that the Pulse was not numbered. It was simply everywhere Ent kind, in endless variation. She wore an Ent crown. It pulsed within her as well.
With this dawning realization, she felt her own heart beat pulsing and all of Ent kind pulsing along with it. Resisting the urge to flee outward, she instead fled downward, deeper into the Ent gestalt, feeling her roots in her own body beginning to fray and tear loose as she did so. She searched for something, she knew not what. A faint whisper of an idea flowed through her head: the thing she searched for was known by the Symbol as a whole, not just her. She let it guide her, deeper and deeper, past experiences no human had experienced before, until Alice ran into Alice.
Alice had never experienced anything quite like it. Deep in her search, she found herself. She found herself searching. She realized that she had been found by her search. She looked up, down, left and right, and saw nothing but herself (did those directions mean anything anyway?). She closed inward, tighter, constricting herself. An animal instinct in her lunged forward in her chest, crying out for her to strike at these encroaching mirages and destroy them before they destroyed her, but she stilled that instinct. It was not the right instinct to use. Instead she/Ents/Symbol reached out and brushed over her head, wrestling her hair from the loose bow that kept it out of her eyes.
The crown tumbled to the ground, and Alice along with it. Her mind, suddenly cut off from the Ents, retreated, unsure what to do in this world disconnected from the Ents. Surely she had seen into the heart of what it is to be an Ent, but one can never be too sure. Her mind ran in loops as it slowly dimmed and the lights went out. Alice's body slumped and rested as her mind fought valiantly to recover.
RedAdler and the Entkind observed this in the same way they always had, discussing those observations as the Symbol of Entkind twisted and turned around them and within them. This one would help, of this they were confident. She had seen enough of what it truly meant to be an Ent to sympathize with what had to be done to preserve their way of life. All that was left was to wait for her to regain consciousness. Fortunately, for an Ent, waiting is.
So they waited.