Have a look at:
Troubleshooting calls in the Your Phone app (microsoft.com)
Some apps may be interfering with making calls. What does this mean?
This error is appearing because you may have paired your Android device to your PC with a third-party app, or your devices may be paired through a pre-installed app from your hardware manufacturer (like Dell Mobile Connect or Virtoo by LG). Some of these apps conflict with being able to make calls, so we recommend uninstalling them, then unpairing your Android device and pairing it again with Calls.
To uninstall apps, go to Windows Settings > Apps >Apps & features. Select the app you want, then Uninstall.
To unpair your Android device from your PC, go to your Windows Settings > Devices > Bluetooth & other devices > Other devices. Select your device from the list, then Remove device. Then, in the Your Phone app, go to Calls and pair your devices again.