The first step is figuring out where she gets the phone. Does she get an allowance and use that money? Stop her allowance. Her friends? Limit interaction with those friends....
You can start by decluttering your room! Take the toys out or anything that looks too childish. If your parents won’t let you sell or donate them, pack them away...
Just tell your friend you think there is a problem, she probably doesn't even know she is hurting you. Say something about it and maybe she can work on it.