Supporting his efforts in phone calls seems innocent enough to me. As long as you don't give him any bad news or anything that might upset him or his recovery. When I was in rehab I looked forward to phone calls to family. And they were very supportive of my efforts toward sobriety. Unless there's something I'm missing, I think it could be helpful for him to have your support and to be able to talk to you.
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You might want to check out our Friends and Families forums. One for Friends and FAmilies of alcoholics and one for substance abusers.