Let's set some expectations
I was bothered by your comment:
I don't just want some boring answer. I want a real life thing that is destructive in a cool way, and if it can be feasibly be harnessed.
Boring (and, in like manner, "destructive in a cool way") is in the eye of the beholder. Please remember from the Help Center, "When asking questions keep in mind that the goal of the site is to help you build your world, not to tell your story." Telling your story is your job, not ours, and rejecting ideas because they're not "cool" enough suggests that you're looking for help writing your story.
In real life Humanity can't harness a "stellar phenomena" to do much more than start a fire. Yes, we could build large mirror arrays that focus on a big lens (I'm thinking James Bond's The Man with the Golden Gun here), but the solution is so honking inefficient that almost any other way to cook (e.g.) meat is used.
But the worst part of your comment is the statement, "can be feasibly be harnessed." Feasible to whom? You? Me? Humanity today? Starting a forest fire is feasible. Punching holes through or vaporizing planets is not. You probably meant "seemingly realistic such that the reader could suspend their disbelief," but even that's a poor restriction. This entire idea is just window dressing for a story. If the story is good, readers will forgive implausible ideas. If the story is bad, it won't matter how "feasible" it is.
As others have mentioned, try to explain as much of the problem, its conditions, circumstances, resources, restrictions, and goals as possible. You'll be amazed by the creative ideas the users here can come up with. But the less you give us to work with, the less we can do. To use a programming axiom, "garbage in, garbage out."
So, having spent a bit of time commenting on your question, which isn't what one is supposed to do in an answer, let's look for an answer. I'm going to pretty much ignore your expectations.
The basic limitation
Drawing on the sun to blow apart a planet is non-trivial. The amount of solar wind — the basic raw material you have to work with — available to you is incredibly small. As-is it can warm the planet to uncomfortable levels, but it won't incinerate it unless the planet's magnetosphere disappears. Now, you could float a Dyson Swarm that could draw enough stellar energy to level a planet... but to do that you'd also have the energy to level the planet in the first place... so why waste time setting up the swarm?
So what makes more sense?
Off the top of my head that leaves two stellar elements that you can work with.
Solar flares. Your aliens have the ability to initiate a solar flare and direct its path. A strong enough solar flare would incinerate a planet, but it's unlikely to blow it apart. (A flare that strong might destabilize the star. And, again, if you have the energy to do that, why bother doing it? Just blow up the planet.)
Gravity.
I think gravity is your better choice, but it depends on whether or not you're looking for a Hollywood-style dead-in-60-seconds solution or a more practical dead-in-a-couple-of-years solution. But I'm voting for it.
The basis behind "warp drive" (like the Alcubierre drive) is to warp space. The cool thing about warping space is that you're warping gravity right along with it. Warp it enough and you get the planet to slide into the sun.
And to do that all you need is, for lack of a better term, an Alcubierre bomb.
Such a bomb would create an intense, localized warp that would seriously affect gravity near the planet. The goal is to move the planet destructively out of its orbit. This has some short-term satisfaction (earthquakes, million-year-storms, global warming/cooling in a very unpoliticized way...), but total destruction would take time. (However, we've breached enough suspension-of-disbelief that it's just a matter of building a bigger bomb, one that might cause the planet to tear in half.)
Why would that work near a star but not in intergalactic space?
Actually, the basic idea would work in intergalactic space, but it would be a lot harder (and I'm bringing this up to make a point about the value of a gravity bomb). Think of the traditional 2D view of the fabric of space. An infinitely long and wide sheet that has billiard balls here-and-there causing the sheet to warp. The more warp you have to begin with, the easier it is to warp it even more. And if the goal is to give the planet enough nudge to spiral down to the bottom of the proverbial gravity well... problem solved.
