Thanks everyone.
I just went around and removed devices and uninstalled stuff and re-installed stuff.
In the end it started to work but I have no idea which of my actions fixed it.
To give you some idea of my setup.
I work from home and have a usb headset which is used for Teams communication with work.
My home PC does not have Bluetooth, so I bought a usb Bluetooth device that is specifically configured to allow for two-way audio communication.
At home I place my android mobile about a foot away from the usb device. The phone connects automatically via the Bluetooth device to the phone link app. Mostly the phone will connect, and I am able to receive and make calls and text messages via the Phone Link app.
In fact, I have just set down and placed my mobile on my desk and it immediately connected to the Phone link app. It's when it doesn't for no particular reason that I run around checking settings, drop and re-install devices until I get it working again. So currently it is working. But thanks to all those who replied to my question. I will consider this question as answered.