I'm sorry to hear that. I'd talk to him for you if I could.
What happens when you try to talk to him? What did he need your phone for? Or was it just to bully you? Maybe he has difficulties expressing his needs.
Have you considered learning self defense or finding friends to help?
It's really frustrating when adults don't help. It sucks that you have to help yourself. You should be able to feel safe and not have to worry about this.
Try relating to your opponent first. Show respect and listen carefully. They might be in a lot of pain and no one is there for them. It's hard and it will test your patience. Think of it like slowing down a ball of anger rolling down a hill. It'll just keep going faster and faster until one of you decides to slow it down.
But after you've done that, you should not tolerate someone who keeps ignoring your boundaries, and make a plan to handle the problem. Stay calm inside and don't hesitate your decisions, and fully commit to your actions.