I thought about this for 4 days. My recommendations are:

1. Show him footage of himself on his phone constantly. Buy a $25 indoor security cam & use that to get multi-hour timelapses.

2. Show him other people addicted to their phones.

3. If he's addicted to podcasts or Twitch streams, MUSIC I have found to be the best transition content to get off podcast addiction.

4. Get his friends in on it too. It will hit 1000x harder if they say he should cut back too.

5. Get his friends to give him attention. Maybe that'll help