Tough one. I'm kind of proud to see your compassion with your uncle.. because honestly, if I were you I would hang him up and block him.

I don't have many suggestions. If you decide to communicate with him via phone, is it possible to you to make a conversation about himself? I mean like one-sided responses, but limit his chance to ask you or gossip by asking more and more about himself. I did this to a NPD and it was always effective.