I want to use my phone as the speaker & microphone for my pc and I think this could be especially useful for some specific occasions.
I've just been looking for a solution to this myself. After some significant searching, I've found that pulseaudio is capable of sending an RTP stream over the network: https://www.tipvote.com/a/linux/10537 It's a bit cumbersome using this method since you have to know your phone's IP address on your home network, manually load the null-sink and rtp-send modules targeting that address, and connect to the resulting RTP stream on your phone via a compatible app, (e.g. VLC or PulseDroid RTP https://github.com/wenxin-wang/PulseDroidRtp/) but it works with only minor latency and very little dropped audio. Perhaps this is coming from a place of ignorance, (I am not a developer) but it doesn't seem like it would be difficult in principle to incorporate this functionality into kdeconnect, especially since it's mainly just leveraging capabilities pulseaudio already has.
*** This bug has been marked as a duplicate of bug 374017 ***