The phone is a kind of shield for the person holding it above their head. It safely removes them from having to fully engage with what's in front of them.

The camera both removes the person from the scene and also by recording enables the event to be captured in a format to be reviewed again. The videos are never actually intended to be watched again or shared with friends though but they are proof that the person was physically there (if not wholly present).

There was a video I recently saw about how birthday parties should be filmed. Instead of a video of just the birthday girl in front of a cake reacting to her friends singing happy birthday, she takes the camera, flips it so we don't see her anymore but we see her friends singing facing her with faces full of love.