I'm afraid I'm with Maynard on this - lifting your phone up to film or take pics at a gig means that the people behind you have to either watch through a tiny aperture, or try to look around it.
Secondly, the quality of the photo/video isn't going to be worth looking at either - low light, fast shutter speeds etc...
Finally bands like Tool spend heavily on their visuals, intermittent flashes and tiny video lights detract from the aesthetic that they're trying to immerse the punter in.
and that's without even considering the legality of it.