What the glance says
You don't mean anything by it. Nobody does. But the glance is received as a message whether or not one was sent, and it's worth being clear about what the message is.
The message is about rank. When somebody is talking to you and your eyes go to the screen, what your face says is that the thing on the screen, whatever it is, outranks the thing being said. Not forever. For the second. But rank isn't measured in seconds. It's measured in who gets looked at when there's a choice, and every glance is a choice, made in front of the person who lost it.
Chotpitayasunondh and Douglas found that the route from a partner's phone use to the worse conversation ran through feeling less that you belong. That's the message landing. Belonging is the sense that you're one of the people someone would turn towards. The glance is a turning away, and a hundred small turnings away add up to a claim, and the claim is "you're not quite one of those people", and it's a claim you'd never make in words.
My reading is that this is why the glance stings out of proportion to its size. It's not the second. It's the ranking, and people are very good at reading rankings from faces, because we've been doing it since long before phones. A child reads it at once. Adults read it and explain it away. Everyone reads it.
There's an earlier book in this series, They can't read your mind, about how the people close to you can't tell what you need unless you say it. The glance is the mirror of that. They can't read your mind, but they can read your face, and your face is saying something you don't believe. The only way to correct the message is to stop sending it, because "I was listening, honestly" arrives after the face has already spoken.