In my story this girl was spying and need to destroy a communicator once she sends a message telling what she learned. Apperantly the people she was spying on caught her. Would she have the strength to destroy/shatter it?
This drop-test video of an iPhone XS shows what happens when you throw the phone onto concrete (at the 5:10 mark). Admittedly, the tester isn't using his full strength, but it's a useful demonstration: not only is the phone not destroyed, it's still usable.
(It's eventually rendered unusable after several more throws.)
However, your character needs to do more than just make the phone stop working; if she's worried about being followed, she needs the computer inside the phone to be completely destroyed. There are some pretty easy ways of doing that, like using a drill or a microwave, but sheer physical force probably won't do it.
If it is a phone, or a phone-like object, throwing it on the ground will likely break the screen, but not the internal electronics.
You'd need to snap it in two pieces, preferably break the printed circuit board, the battery, or the internal power connectors. Hard to do by hand, and potentially hazardous as snapping LiPo batteries in half may result in flames. You could set it on the ground, with one end resting on an object (like a curb) and stomp it. Less risk of burns.
Now... Electronic circuits and printed circuit boards can be washed in water without damage if they are not powered. But if they are powered, water will cause electrolysis which will destroy printed circuit board traces and tiny components in minutes. This isn't spectacular, and doesn't create sparks like in movies, but the device will cease working.
So, if the device is not designed to be waterproof, completely destroying it may be as simple as just throwing it in a river, in a toilet, or just in the sink with water running on it.
If it is designed to be waterproof, then of course it won't work... but if it sits at the bottom at a river, it will be unable to transmit, which may be enough for your plot purposes. Also, readers will understand that water destroys electronic devices.
This won't destroy the flash chip itself though. If you really want to shred the data, the best would be to throw it in a fire or ... blend it.
TL;DR she needs only destroy a part of the phone, not all of it.
I think the essential part she needs to destroy is the data records of her actions, and the way to contact her allies.
In phones of modern times, we can store our data on hard drives or even portable solutions, such as an SD card. Some of today’s modern phones support plugging in external SD cards. If she has her world’s equivalent of an SD card (some small automagically storage device that inserts into the phone) she could easily remove it from the phone and snap it to pieces. As @arp mentioned, simply snapping it may not work, but an SD card is small enough that a few hits with a large stone or heavy object like a fire extinguisher would easily pulverize most of the parts inside. See here for how the flash memory of an SD card works. As long as the memory of the card is destroyed, all the stored data would be irrecoverable. This would destroy all evidence and would be physically doable by even a ten year old.
If she just stores her contact information or app that is used to contact her allies on her SD card, it would prevent the enemies from accessing any data for a while.
Anyone who says no has never had a toddler throwing a tantrum throw an iPhone. They break every darn time. 15 year old girls can manage a decent fastball (my gf in hs could do 89mph a couple times in a row). It is absolutely plausible for your heroine to break a communicator.
Edit: that does not guarantee that all of the data would be unrecoverable.