I am just constantly in wonder of how pathetic and weak-willed someone must be to have their enjoyment of a concert ruined by someone else in looking at their phone. I would think the ego stroking of getting to declare someone else "not a tr00 music fan" and yourself, by extension, better would be the sort of thing that would fuel many of your fragile self-esteems for another day.
if they were looking at their phone, as in checking their message or surfing the web, i couldn't care less.
the problem, for me, with phones at concerts is that people use them as aerial recording devices: they hold them up over their heads, i.e. in my line of sight if they are in front of me. i'm mildly photosensitive and the glare of someone's screen (why the eff does everyone have their screen brightness cranked to 100%?!?) diminishes my ability to see the show. i'm paying to see musicians on stage, not a thousand points of light. if it was limited to sticking your camera up, taking a pic or three then putting it away, it would be a mild nuisance. but folks are holding their cameras up for minutes at a time, if not the entire show.
and let's face it: how often do folks go back and watch their grainy concerts vids with unlistenable audio? there is a chance you
might watch it again, meanwhile you're
definitely disturbing me. some might see is as "it's a free country, do what you want". i believe that "do what you want" should be moderated with some consideration of those around you but YMMV.