When I was in highschool I had an app to help calm me (recommended by my therapist) because I had such severe anxiety problems. I know there are things you can do without an app but it was helpful when I was panicking so much I could hardly think. I don't think a blanket ban is appropriate. Phones aren't inherently bad and it really depends on how they are being used. It makes more sense to revoke phone privileges from individual students if they can't use them properly.