RTMT is not the correct tool to use for call reporting - it is more of a system health and troubleshooting tool (but it does ALOT, and is very useful).
The built in call reporting tool is called CAR, and can be accessed inside of CUCM by going to:
Cisco Unified Serviceability -> Tools -> CDR Analysis and Reporting
From the dropdowns at the top, you can run user reports on the number in question.
If you're looking for something more user friendly, you could try VoIP Detective. It's a free CDR reporting tool that will allow you to pull reports using CUCM's CDRs.