It's not a jealousy thing, and honestly I don't think it's just about social media addiction either, even though that's part of it. The real issue is that he's not seeing the emotional impact it has on you, because for him it's become so automatic that he doesn't even notice it anymore. When you say "you're ignoring me," he hears it as criticism, but when he says it's just a habit, he's not minimizing your feelings - he genuinely doesn't realize that habit is affecting you.
Try bringing it up at a time when neither of you is on your phone and not right after it happens (so it doesn't feel like an attack). Tell him something like: "when we're together and you're scrolling, I feel like what I'm saying doesn't matter to you." It's not a complaint about his habit, it's about how that habit makes you feel. Sometimes guys understand the language of feelings better than behavioral criticism. And maybe try suggesting something concrete to do together - a dinner without phones, a walk, something where it's physically hard to be on social media. Not to punish him, but to let him experience what it feels like when you're actually present with each other.
If nothing changes even after you try this, then yeah, the conversation gets more serious and it might be worth asking yourself if you're on the same page about what being together really means.