DS is 13. He's had an old IPhone of mine since he started secondary. He is on it a lot: he and his friends seems to be in constant, chatty, contact whenever they aren't at school. It gets turned off / put away when he's at school (not allowed to have phones except switched off and in their bags on school grounds), homework, eating meals, reading, watching a film / telly with us, and going to bed / overnight. But otherwise, it's usually on.
He has a friend over today. They are playing on the Playstation, taking turns to play Fortnite. When his friend is playing, DS is messaging other friends, watching TikTok videos (occasionally showing one to his friend) etc. To me it looks really rude and anti-social - like he's ignoring his friend who is in the room. But he - and the friend - tell me it's totally fine, it's what people do these days, and anyway his friend is playing when he's not, so it's not like his friend can chat anyway.
A friend teaches in a college and she had reason to ask her 16-17 year old students if it's normal to do more than one thing at a time - like watch a film but have their phone on at the same time, or be out with friends and scrolling through messages from other friends at the same time. They assured her it was totally normal!
Am I way out of touch?? It looks so anti-social to me. I would never have picked up a book and started reading if I'd had a friend over as a child.
YABU - it is totally anti-social and teens should not be constantly on their phones when they are in company
YANBU - it's normal these days for teens to have their phones on even when they are with friends and are doing something with them (but you don't have to like it!)