Eye contact is the receipt that proves you were paying attention.

Looking at someone is the simplest available proof that you are in the room with them rather than half inside your own head, and its absence reads as distraction even when you followed every word. None of this means staring, and some people find it hard for reasons that have nothing to do with interest. What matters is that the visible signal matches what you are actually doing.

Try it in short stretches, especially when someone reaches the part that matters most to them. Put the phone face down first. Look up when they finish, before you answer.