A lost phone keeps buzzing with people who love its owner. Answer one of them.

A lost phone is not an object so much as a panic in progress. Somewhere a person is retracing their steps, and the buzzing in your hand is their family trying to reach them. Once you picture that, the question stops being whether this is worth your afternoon.

Answer the next call that comes in and say where you are. You do not have to track the owner down yourself, just hand it to a front desk and say where you found it. Five minutes of yours, a whole evening of theirs.