Usually I answer calls with the standard iPhone receiver. Sometimes, while the phone is charging and I'm in the other room, I have to answer the call with a bluetooth-connected smartwatch (otherwise I wouldn't make it in time,) then I have to run to the other room and press the speaker button to start the conversation.
Note: on the smartwatch I just press "answer call" but it has no speaker, so the call is completely handled by the phone itself.
I know it is possible to route audio to the speaker by default, but is there a way to do that only if I'm triggering the "answer call" from the smartwatch?