I need your opinion!!!?

Ok, so here is the story. I am a stepmom to a 16 yr old that I am raising by myself. His father is in jail and his mother doesn't want him. So he and I have ed heads for months because he thinks that he can do what he wants when he wants and doesn't have to listen to me because I am not his real mom. But, I have raised him the last 8 yrs so ya I am his mom. So the other day he got pissed off and decided that he was going to get out of the car as we were driving, I told him if he got out of the car he would have to deal with the consequences, he told me that I couldn't do anything to him. Well, I turned his cell phone off. The next day he came home all was fine until he asked me when he got his phone back. I told him I didn't know? He flipped out and punched a hole in the wall. My daughter got scared and called the cops because she was worried about my safety. So now we are 4 days after that, he acts as if nothing is wrong and he did nothing wrong. Wants his phone back and I won't give it back because I don't think he deserves it. Am I over reacting?