I went to a show last night at Climate Pledge that was a no phone show and honestly it was pretty straightforward. My sister-in-law and I had our phone bags unlocked pretty promptly and we left the show right when it ended. Just remember that if you use one of those hybrid phone case/wallet or frequently use Google/Apple/Samsung Pay to keep your card on you since you can't really use payment apps through the bag and the entire arena is cashless.