Half here, half in your phone is just lag in real life. The people across the table can feel the delay.

Divided attention is visible from the outside even when you think it is not. The half-second delay before you answer, the reply that lands slightly off the point, the eye contact that keeps resetting. The person across from you is not so much offended as informed. They can feel that they are the second thing in the room.

Put the phone somewhere else for one conversation today rather than face down in your hand. Notice how much more of the other person you get. This is not about how much you use it, but about not being in two places while somebody is talking to you.