I’ve got a few automations on my phone for this situation, if airplane mode is turned on it will lock the screen, turn airplane mode back off and put the phone in low power mode. I also have it set so if I text it a killphrase from any number it’ll lock the screen, low power mode, bluetooth and cellular on and then reboot. Apparently rebooting makes iPhones much harder to hack 🤷🏻‍♂️