"Never mind confiscating a phone, we can't even delete a picture when a patron is caught taking one. The patron has to do it themselves while house staff watches."
...and it's satisfying to have them do.
And, honestly, nearly everyone I have asked to delete a photo does it without much of a fuss. People ask and I explain the copyright issues, which many of them have never even considered.
"...everyone finally shut up, and the audience could enjoy the beginning of the Anatevka Pogram in peace."