I'm aware of the gesture on the fingerprint sensor and I can say with absolute certainty that I'm not accidentally touching the sensor. As to the tip of my ear that is a possibility since it's my ear that is touching the phone at the ear speaker area when it happens. But shouldn't I be able o have my phone to my ear when on call?
Start a telephone call, preferably to someone you know that you won't have to waste time actually speaking to. Call your wife's phone, or maybe a time service like this one
https://www.aarp.org/work/on-the-jo...rvatory's time,by the U.S. Naval Observatory.
Anyway, once the phone initiates dialing, sit it down on the table and hover your finger over the proximity sensor (near the speaker) to determine it's range and, in particular, it's side-to-side sensitivity.
I find that on my 4XL I can easily drag down the notification bar from near the left side of the screen without triggering the proximity sensor. This approximates the motion I first suggested, your ear tip contacting the edge of the screen before the proximity sensor is close enough to be triggered.