Does it seem wrong that I secretly threw my bully's phone out of the window on summer camp
Why did you throw out your bully's phone?
I've had enough of his shit for almost half year.
While it isn't good to damage someone's property, it is understandable since you were being bullied.  But, two wrongs do not make a right.
I didn't buy him a new one, it's not like I care about him
Although you may feel justified for your actions, you should avoid damaging other people's property. It would be best to assert yourself instead and speak up about how you feel.