

I am doing this and it works quite well. My PC shows up as a headset on my phone and i connect to it as such. I dont have any custom software for it so its very basic and i still have to pick up the call through the phone, but once i pick up it uses the audio input/output of my desktop machine. Im on debian 12 with KDE, but i assume it should be just as easy on ubuntu.
Previously this required some tinkering, but on my current setup it just worked out of the box. Just make sure your computers bluetooth is set to be visible to other devices, then it should pop up on your phones bluetooth search list. Make sure you give the desktop phone call and media permissions on your phone.
If this doesnt just work ootb, then you might have to change some config files to enable it, but there is lots of information out there if you look for something like “linux/distro bluetooth as sink”