they just lose interest when it isn't their turn

Well, reflect honestly on your games. Can you blame them? If they aren't being prompted for their input, why should they be paying attention? Is there something they could actually be doing if they were?

When players start stacking dice and playing on phones, it's a huge red flag that your game is boring and you need to cut out the dead time and give them more to do. Unfortunately this can be difficult with games like D&D, especially in combat, but it's still doable. Speed it up, give people more to do, and be more engaged with THEIR ideas.

Yes, it's rude to sit there on your phone when you should be contributing. But if you invite people to game with you and then completely fail to give them things to do, that's your fault, not theirs.

A lot of GMs tend to lose touch about how their games feel on the other end for the players. The GM may be doing a bunch of different things and feeling engaged the entire time, but the warrior who just rolled a d20 to attack on their turn, tried to do something cool but got told no, and then has been sitting there for 20 minutes for his turn to come around again has every right to be on his phone.

How I've changed to combat this problem: I keep my groups small (5 players including me, max, no exceptions), shoot to wrap entire globetrotting campaigns up in about 5 or 6 sessions, and I view my main job as GM as pacing the story and keeping all players prompted for their input which then directly influences the narrative and the game. I prep very little and accept their ideas almost wholesale. There's no sign of a phone anywhere because everybody is constantly engaged. I think most people are surprised by how fast and engaging RPGs can be, but you have to let go of some bad habits and maybe update to a rules set that makes the task easier.