In a perfect world, nobody should have to police anybody else in the theatre. Everybody should know that using mobile phones to text is as rude as talking throughout. Mobiles should stay off and out of sight, unless they are part of the performance or have been sanctioned by the theatre and are being used from specially designated tweet seats so as not to cause disruption to other members of the audience.
But they don't. There are plenty of people who seem to think that they haven't actually experienced something unless they have photographed and videoed it – and that extends to their theatregoing. I have seen members of the audience blatantly video the whole of both Dora the Explorer Live! and Jesus Christ Superstar, and ushers have watched them do it, entirely unperturbed. Maybe people are confused. If it's all right in Dora the Explorer, maybe it's OK in the new West End production of Passion Play, too?