The person who checks their phone mid-story teaches the storyteller to stop telling them things.

Every glance mid-sentence sends a small piece of information, and it gets filed. The person telling you rarely complains. They shorten the story, skip the part that mattered, and eventually save it for somebody else, so you lose the news, the invitation and the thing they were working up to saying, without ever finding out you lost it.

When somebody starts talking properly, turn the screen face down without announcing it. Ask the question that proves you were following. If you really are waiting on a message, say so at the start rather than reaching for it halfway through.