I wouldn't actually do it, but I am tempted sometimes.
My son has a card that entitles him to have someone to accompany him, which is usually me. He likes horror films, but I don't.
So the person on the phone might, in some circumstances, be the companion who is there because their loved one wanted to go but has no interest in the film.
Doesn't excuse them though, it's very distracting and I wouldn't do it. I just shut my eyes and think of unicorns and fluffy things.