Laketime,
I am glad that your son made it to the Oxford House. That is a good step. If you turn his phone back on is there anyway you can have it for only certain numbers? I know there are phones for kids that they can only call numbers the parents put in the phone. That might be better this way he can only call you and your husband and maybe a good friend who is clean. This way you are doing something but are limiting it also.
Look to your HP for him to guide you on this. The right answer will come.
Hugs,