On calls coming in from outside to your PBX, the number of the other party is shown on your screen.
If you use Asistan34 Call Center Customer Tracking CRM software, you are in luck.
If the caller is a debtor and the phone number they are calling from is registered in a debtor file, their first and last name also appears next to it.
When the call is answered, all debtor files associated with that number open automatically on your screen.