Same problem. Everything works fine for texts. The phone function used to work through my PC, have a USB connected Mic that used to work. Now it forces audio to my Pixel mobile phone in the phone's settings. When I tell the phone to use the PC as a speaker / audio device (similar to how you might have to divert a call to your Bluetooth headset), it immediately snaps back to the phone's default setting.
What they need is an in PC app audio setting page where you can firmly mandate which devices serve as mic and audio for the app. Like pretty much EVERY normal communication and recording app but this one. Discord is a great example of doin this right.
As it stands, the call function is nothing more than a glorified dialer for my mobile phone. What is MS thinking?!?!