What should my friend do?

Hi, I’m asking this question for a friend at work. He currently has an 8yr old son that lives in Tennessee and my friend lives in Florida. His sons mother is an alcoholic and is becoming progressively worse. His son tried calling him yesterday to tell him something happened and his son sounded scared. His sons mother interrupted the phone call and wouldn’t let them talk. Now she’s not letting him talk to his son at all. There is no custody agreement since they were never married but she did file for child support and he is current on that. I have him calling about legal advice today on how to get his son out of the situation but I don’t know if anyone has dealt with this before and can offer any advice. I just want to help his son and he’s worried for his son at this point.