I regularly see people on their phone even at the movie theater. Rarely are they actually on a phone call but they’re checking the time, sending a text or doing something else that involves taking the very bright screen out of their pocket and holding it in front of them. In a darkened movie theater, this is very distracting for the rest of us, even if they are five or ten rows away.
In that respect, home viewing is better, but my living room can’t be darkened as much as I’d like.
People are rude idiots, and mobile phones should be banned/confiscated/blocked/destroyed upon entering any public venue. I hate the goddamned things.
Dimwits who pull them out in a darkened theater deserve to be treated like smokers who light up, preferably with a good smack to the head.
I pay slightly more attention in a theater, but it’s not significantly different. I need to pay attention to enjoy the movie, unless I’ve already seen it. And if I’m not there to enjoy the movie, I might as well do something else.
The only exception is this one time at a (dormroom) party. When the girl who invited me decided to sit on my lap, my attention was diverted. But I don’t think that counts as a normal circumstance.