Cell phones on a stand is very common these days even in the most professional rehearsals and performances. For one, many use them as a tuner. Even in my time with the national tour of Lion King, as soon as a number was through, phones came out. In a show. Granted it was in a pit where couldn't be seen by the audience, but it still was just part of playing that show as long as many of them had been. I honestly feel if you can play your stuff and its not a distraction, then it's whatever. For years people would read a book in a rehearsal with a long tacet, the older generation needs to adapt that phones are a part of our culture especially with a smartphone. And the younger generation needs to do a better job of not being obnoxious about it. Theres a middle ground.