You can't even trust that it's your phone; it wouldn't be that hard in many cases to provide an identical-looking device that just records the entered PIN. It won't hold up to inspection once unlocked, but it doesn't have to; once you've provided the PIN, you've lost.

If the device has left your possession, don't accept it back or interact with it. Get a new device, and restore it from backup.

Also, if you fill out the emergency contacts in your phone, you can call those contacts without unlocking your phone.