So... I already know the answer, but I'm going to throw the question out there anyway because I'm a slow learner .... Is there anything I can/should say to diffuse h a bit? Yup... He's still on the lets be nasty to Feyth freight train.
Yes .... you need to start your boundaries. During conversation the second my MLCr started to insult/spew/monster I would give her one verbal warning "I am not going to continue being treated like this, if it continues I will end this conversation" ..... she would continue to blast and I would walk away/hang up whatever. This continues but eventually she would quickly stop ... and it would take a bit to crank up again but once it did I would end it. I held FIRM to this approach, she was conditioned that if she monster'd in my direction the conversation was over and I can not tell you the last time I had to end a conversation in this manner.
He will test, may blow your phone up, follow you, what ever .. .just continue to walk away and refuse to say another word. Its hard at first but honestly this was one of the best things I ever held to during the crisis.