It's harsh that you and your son have to listen to this ramble. I would encourage your son to end conversations with his dad asap if he is drunk, simply ''I've got some stuff to do, speak to you later'' or something, does he go to ala-teen or some other support? I just feel bad for him that he is spending so much time on the phone pacifying this drunken father.
My heart goes out to you both,
I hope you both find a way to deal with this that allows you both to keep you serenity,
Blessings
Lily xxxxxxxxxxxxxxxxxxxxxxxx