How does iOS know which apps can receive “calls”?

This morning, out of the blue, someone I know called me -- on Facebook Messenger, on my iPhone. I was happy to hear from him, but also puzzled: I have all notifications for Facebook and Messenger turned off, and I wasn't even AWARE that a "call" function existed for Messenger.

I also have a softphone tool on my phone (Nextiva) plus Teams, for work. I can receive "calls" via either of those tools, too. In those cases, that behavior is welcome; not so for Facebook. It wasn't until today that I realized "gee, I never told my phone to let those things do "call" behavior".

Is there really not somewhere in the iOS settings where I can control whether or not an app has access to telephony-style behavior? Or have I just missed it?