can't hang up phone calls

I've recently started experiencing a problem with my iPhone X (current iOS) where I am unable to end a phone call. I have to wait for the other party to hang-up. More specifically:

During a call I'll go to the Phone app's keypad screen, intending to locate and press the red phone icon at the bottom to hang-up. However, the phone icon at the bottom is green, not red. That makes no sense. The icon should not be green when I'm in a call (a green phone icon is obviously for an inactive phone to place a call).

In other words, during a call the keypad's hang-up button (red phone icon) is not present. Instead the call initiation button (green phone icon) is displayed.

Even though it's green (when it should be red), I've tried pressing it anyway to see if that will terminate the call, but it doesn't.

I've seen a few other threads by people who are unable to hang-up, but the details of their issues are slightly different than mine (which is why I started a separate thread). For some people, they are unable to wake the screen during a call. To be clear, that is *not* my problem. My screen wakes up. For other people, they are able to get to the keypad screen and see the red phone icon, but pressing it does nothing. Again, I'm not even seeing the red icon -- mine is inexplicably green (as though I'm not even in a call).