You have every right to have NO CONTACT WHATSOEVER with him. No contact NOW, while he's on his contraband cell phone. No contact IN THE FUTURE once he's out of rehab.
As others have said, nothing has changed. If he truly wants recovery, that is on HIM. There is nothing that YOU can do to either help him succeed or cause him to fail.
Have you looked into Alanon? One of the things you'd learn there is the 3 C's:
You didn't CAUSE his drinking.
You can't CONTROL his drinking.
You can't CURE his drinking.
Hope you keep reading and posting here and I also hope you get to Alanon for some f2f support and education.