unable to use inbuilt mic while mic-less headphones are plugged in for phone calls...

I did notice that it worked somewhat, albeit quietly, to set the software to use speaker first, then while on the call turn speakerphone off. I could then hear the 2nd party thru my headphones and 2nd party can hear me thru speakerphone. This is not ideal, needless to say...

Any help would be greatly appreciated!

That's odd. I've been able to use a headset (no mic) and use the phone's built-in microphone.

I've been fixing some issues that were tough to find the past few weeks and am just getting back to answering emails/messages.

I just uploaded a new Beta version here.
https://soundabout.forumotion.com/f8-download-beta-versions

Reboot after installing.