I know this is hard. I remember those overwhelming feelings.
I would not answer his call. You already know he's been drinking.
Do you like imagry. I don't usually but I have found it really helpful in the last 6mos. I think it works better for me when I am in such a state of anxiety and confusion.
So here is one I use. I pictured myself building a wall. It was my boundary. (So in your case you do not speak with him on the phone when he has been drinking.) So I picture myself leaning on this wall, with the warm sun on my face. I am warm all over and I'm doing something totally nonchalant, like filing my nails. I am unconcerned. I'm leaning on my wall, holding it up. He's on the other side. Sometimes he's just sitting there looking pathetic and sometimes he's having some kind of tantrum.
The wall, my boundary, keeps me serene and he is left to deal with his own self. Before I made concrete boundaries for myself the walls were more like speed bumps and he lobbed all the bad stuff over on my side. He was calm, I was nuts. My boundaries help me keep my side of the wall warm and safe. Slowly my internal feelings were in closer alignment to the woman in the sun filing her nails.
I also use the image to not react to the anxiety. My job is to keep the wall there. To uphold my boundary, regardless of the anxiety, which was extreme at first. To breach the boundary would mean I had to knock down a peice of that wall and this image is so powerful to me that I can't even make myself start tearing that wall down in my mind. The minute I start thinking that the sun begins to go away and if you knew me, I love the sun and hate a damn cloudy day so I immediately stop the hammering and let the sun shine down!
Not that I don't make mistakes but it gives me a lot of strength to listen to my head, and not my anxiety.