Assuming he’s with other people when using, he’s probably too busy chatting to be on his phone. My husband used to be the same when he was using. He would be on his phone a lot day to day, but then not when high/out. Its because they have something else to do.
One of the other things I found out, was that he was spending a lot of time messaging the other woman, but wasnt online because he was with her! But thats only my experience, i’m not suggested you’re in the same boat with that one.
Sending love x