Stream airpod audio to iphone XS bluetooth speaker

Hi

I would like voice audio generated through my airpods streamed to an iphone XS bluetooth speaker (or even just the iphone's own speaker).

Everything connects fine, microphone output works when I make calls and the bluetooth speaker works when I play music, but I am not sure how to stream directly from microphone output from my airpods to the bluetooth speaker.

Is there an app I need to use to provide the interface between the two? I tried 'Microphone' but that didn't recognise my airpods as input devices.

Many thanks for any suggestions.

Meridia