Hi hummingbird, Have you contacted the staff counselors at his treatment center about these phone calls and what he is saying? If it were me, I would make sure that they absolutely knew about his suicidal ideation.
Edited to add that coming off of alcohol is probably the hardest detox. I would imagine he body chemistry is in a state of flux right now. It's one of the reasons why a medically supervised detox is always advised. My stepson has been detoxed in a hospital about 4 times. The first time he was very depressed, combative, even. He has been in full-flown DTs a couple of times --once while walking the streets of the city where he lived (luckily some friends found him and took him to the hospital).
I'm so sorry you are all going through this! You remain in my prayers.