Look up "phone free" and you'll find the references. What it is: It's a strong fabric case that locks you out of your phone with a very strong magnet.(defaces the object you have) This prevents you from answering the phone, making calls, using the camera etc. Have a medical/police/medical-staff being called back emergency? Good luck buddy, no one cares about this.

The company who is doing this is Yondr. They've been doing this for years. They've been doing this with musicians, comedians, courtrooms, and even at schools. I'm amazed that they have been getting away with this for so long.

Yondr has had a lot of astroturfing over the years so it's harder to find the people who have had a bad experience over the years. You'll see non-normally participating people pop up in every comment section that mentions the phone ban: "well i like that everyone isn't on their phone" etc. Also, you'll see near promo news pieces on this. Additionally there has been no public comment with this that I know of, which is super auspicious from the US or Europe. (Just did the research Placebo and Bono have enforced this in Paris.. a bit brave considering the bataclan)

EDIT: Dang, yes I said the a word (ends with turfing), this is not a statement thats happening here.

Not OP but there are a few performers who like to either confescate phones or place them in locked baggies to stop the people who hold their phone in the air filming a video nobody will ever watch.

In theory I like the idea but in practice I agree with OP.

Never seen it happen at concerts, but it happens more often than not at standup comedy shows.