I'm annoyed that my estranged dad is trying to buy me a new phone.
Why does that make you annoyed?
I just want to live with my mom in peace and I do not need his help.
I know it is awkward to receive a phone from your estranged dad when you don't want his help, but it's still good to feel grateful when someone gives you a gift. Maybe he's looking for a way to get back into your life, and build a relationship with you.
I don't want his phone and I'm never going to forgive him.
It might be a good idea to tell him you will take it, but you need more from him to get him back in your life. It was nice of him to do that and you should at least be a little thankful, even if you aren't necessarily ready to forgive him.