For me it's not even a conscious effort, as it feels rude to be on your phone, when you are having a meal with someone. Is it not rude to start reading a book while you are having a lunch with someone, why is the phone any different.
When there is a need to look at your phone (Important message, a call, or even to look up something), I think the polite thing is to excuse yourself, do the thing really quickly, and get back to your meal.
When there is a need to look at your phone (Important message, a call, or even to look up something), I think the polite thing is to excuse yourself, do the thing really quickly, and get back to your meal.