This has been a problem for years. Please tell the developers to update the app with IN-APP AUDIO SETTINGS that allow us to choose the input and output devices on the PC side for making calls with. It's not enough to use the default or default communications device. Some of us have very complex audio device setups, and can't compromise over this app alone. I do music and sound professionally, so if I have to undo my setup for all that just to make a phone call, it's a problem with the app asking me to do that.
Edit: I should note that the app (Phone Link) also does not show up in the system's (Windows) audio settings, where you'd at least be able to change the output device for it, as you are with any other app. It doesn't even show in the add/remove apps list. It shows only as a system component, which doesn't get any of those options. There are no easy workarounds for a feature that the app should have, but inexplicably doesn't.