I'm really annoyed that my girlfriend still hangs out with and talks to her ex every day. I want to stop it.
Oh wow. Does it make you uncomfortable? Why do you want to stop it?
I feel that he is trying to control her life by making her do what he wants her to do. He's the living incarnation of a controlling person.
I can understand that you might be feeling a little jealous. I think you should have trust in your relationship and avoid telling her what to do. I'm sure she wouldn't do anything she didn't want to and you should talk to her about how you feel.
I feel that he's controlling my girlfriend. I'm going to get her a new phone soon, so she loses his number.
I think that's a bit extreme to do and really shows that you don't trust your partner. Have faith in her to choose her friends and be honest with you or you'll be sabotaging the relationship from the inside. You should also not tell her what to do by saying she can't talk to him and instead just sit her down and let her know how you feel.