Don't be ridiculous. Fear of terrorism is not the only factor. Cellphones are one of the past century's greatest contributions to public safety.
If you want to be antagonistic about the threat of a bombing, how about a more commonplace example: you're a very drunk young girl who's been separated from her friends at the concert and a pushy, aggressive guy you don't know is trying to get you into his car to go home with him. You can't text your friends that you need help because your phone is locked.
Or how about this? You're a parent and you've lost track of your kid in the sea of people. You can't text or call them, because your phone is locked.
Or how about this? You're alone and you have a medical condition and something goes wrong, and you need immediate attention, but you can't call 911 because your phone is locked. Your only option now to hope someone else in the crowd notices that you're passed out on the ground not from drunkenness, but from something much more urgent.
Don't act like cellphones have no practical use and are just social media machines. How absurd. They save lives every day and this policy is insanely dangerous for everyone. People here saying "How did people survive before cellphones," well, guess what, in many cases they probably didn't.