Hello,
Even though this kind of situation isn't something thematic to the forum, I feel for you so I will try and give you my perspective in hopes that it might be useful to you in any way, with the strong caveat that I'm not a psychologist or trained in any type of therapy, I'm just someone that is somewhat addicted to certain types of entertainment as well.
Phone addiction is very widespread right now, especially among the youth. In your case, you've been together for many years now, which means you should be able to have an honest conversation and be vulnerable with each other. Sit down with him and try to figure out what the root of his addiction is. Instead of pushing how you feel on him (even though that is obviously important), try to approach it from an empathetic perspective first - is something missing from his life that he finds in his phone in one way or another? Is he hiding from some emotions? What is it that the phone is providing him with that you or life in general aren't?
Once you have the answer to that, you should be in a better position to understand the situation better. Whether you push the way you feel into the spotlight at that moment depends on what the root of this addiction is. In any case, if he truly cares about your relationship, he should be able to understand where you're coming from and why you're even talking about this with him. There is no easy way out in most cases, but at least if the root is something that is missing in your relationship, which he finds relief from in the digital world, then you can both work on this and gradually pull him out of it.
In any case, it's important to approach this from an empathetic side, from a place of love and care, not from a place of judgement and blame. I hope this resolves in a positive way and you rekindle the fire of your relationship. Take care
