Paul Syverson once put it, "there's no such thing as perfectly secure, there's only secure enough for your purposes; so figure out what your purposes are, then plan accordingly."
There’s no such thing as safe opsec, just safer opsec.
If you can help it, don’t bring a phone to the protest.
If you have to bring a phone, use a pin to lock it.
If you have to use biometric unlock, turn off your phone if shit is popping off (most require pw on boot up / decrypt)