One doesn't get addicted to the phone, but an activity on the phone. Is it Gaming? Gambling? Social media? Netflix? ******? Work emails? News?
Key will be to find the root cause of the addiction, and find ways to solve it.
Otherwise it might be more macro - maybe he's lost all interest in you, family, socialising. What does his behaviour say when he's not using his phone? Does he immerse himself in solo activities or actively participates in social activities?