Question
How can I select a specific audio device before placing a call on my iPhone, without setting a new default device?
Background
During a call, I can route the audio to several different devices - my iPhone's speakerphone, various Bluetooth devices, iMac, MacBook Pro, etc. This works well when switching devices during the call. I can also easily answer a call from any of these devices.
However, I cannot figure out how to select another device before placing a new call, and just for that call.
Use Cases
My most common use case is when I'm already listening to audio on my iMac or MBP with (wired) headphones and need to place a call that requires me to continue using the headphones connected to the computer.
If I place the call first and then switch the audio to the computer, the other party often answers before the switch completes, and I've missed the first part of the conversation.
Same thing if my phone is mounted and/or charging and I want to place a speakerphone call - if I don't switch the audio before the other party answers, I'm left with an awkward hello...
Context
I'm normally using an iPhone XS with iOS 14 or an iPhone 7 with iOS 13. I don't want to switch the default device since there are many times I'd prefer to initiate the call normally, i.e. phone-to-ear.