I only go to a couple of shows a year (on a good year) and not once has a phone ruined my enjoyment of the show. Personally I don't take out my phone more than a few times, mostly to grab a photo for Instagram, and maybe text or tweet between openers.
It's harder to take a risk with a new song or different show ending because you'll be judged immediately and forever on everything you do. There's a lot more pressure to be perfect at the first performance.
I went to a show earlier this year and the artist had everyone put their phone away for one song. Was great and the audience generally accepted it for what it was, a moment that the artist wanted to share with the crowd.
Just don't treat us like little kids.
(And before anybody asks, yeah - if your friend bought you that ticket with those T&Cs and didn't tell you, that's still not the artists problem... Cope, or get better friends.)