How to turn on Wi-Fi Calling in Google Pixel 1 (not XL)? As a preliminary question to Wi-Fi Calling feature on Pixel - How do I tell if it is using it?, how and where does one enable it in the first place?

Should it appear in the phone app's settings or in the general settings? Can you post a screenshot?

And does it only appear in either of them if the phone company supports it for this phone?
Yes the Mobile Network needs to support Wi-Fi calling.

From Settings -> Network &amp; Internet -> Mobile Network -> [tap on]Advanced and scroll down a bit you should see something similar to the following which was taken on a Pixel 2 with Android 10.