Yes, that’s an annoying trend - okay, not new anymore but I hate it when the players or I are speaking and one or two players are looking at their magic mirrors. I have the feeling - if I‘m really correct I can’t say - that these players are not interested in the game. And of course this magic mirror viewing is very disrespectful.
Yeah, it's very disrespectful, but I don't think it's disinterest. They just don't realise what they're doing, and it's become a habit for so many people. They probably get that bloody device out on dates. That little thing keeps buzzing in their pocket, begging to be looked at.
The challenge (if they don't agree to keep the phone away in a bag or out of sight) is to keep the story engaging and moving quickly, especially combats.
The only game I've played where I didn't have players constantly checking their phones was Blades in the Dark (but only with 3 players). Because so much of that game (story, combat, everything - the GM doesn't even roll) is driven by the players, and we had a small group, it kept everyone's interest.
I think smaller group sizes (3-4) and true player-driven narrative are really important factors.
Unfortunately, my two groups are rather big...