Delete the phone from the radio and delete the pairing on the phone and try again. Be mindful to answer YES to the popup asking about contacts.
You can also tap the gear icon for that device under the Bluetooth Screen you'll be see and make sure that the device is allowed to make and receive calls. able to
If all of the above doesn't work you can try Settings->General Management->Reset->Reset Network Connections to reset your Bluetooth.
Galaxy S21 Ultra 512g(VZW), Galaxy Book (original, VZW), Tab S8 Ultra, Tab S4, Galaxy Watch3(VZW), M8 Smart Monitor