To add an extra layer of safety. Bring a secondary phone when travelling by airplanes, especially to other countries. You should also use it frequently, maybe with some side apps to make it look like it's your daily phone.

Or, just don't bring a phone if you're particularly vulnerable. What are they going to do? Deny you entry because you don't carry a phone? If we're really at that point, where merely not having some item is suspicious, we're in deep shit.