Well, I came upon my first real hurdle, since swapping to my iPhone.
I regularly use a Bluetooth headset (Samsung Galaxy Buds+) and when I was out walking, I received a call. I picked it up by pressing on the surface on the earbuds, but it went dead. Took off my gloves and fished inside my jacket for my phone, it had taken the call, but disconnected the headset.
It turns out, that the iPhone defaults to the internal speaker and microphone, even if you are already wearing a headset with speakers and microphone!
Nothing under BT settings, nothing under the Phone app settings. In the end, I did some searching on the Internet and I found the solution…
It isn’t under audio, Bluetooth or the Phone app, where you would assume it to be. Oh, no, it is much more (il)logical than that. It is under accessibility settings, under Touch! Yes, the default audio device for the Phone app is under touch settings for accessibility!
That is so logical, I don’t know why I didn’t think of it myself! /s