The proxy server is in service to the following On-Premise business cases:
- SBC Routing based on LDAP (AD) in Microsoft Teams
- Updating AD for Extension Dialing for Auto-Attendants in Microsoft Teams
- Hybrid CUCM and Microsoft Teams Dial Plan Management
Read more about the Proxy Server 
Connectivity to Active Directory (AD) and Cisco Unified Communications Manager (CUCM)
Hybrid CUCM and Microsoft Teams Dial Plan Management
This feature streamlines the management of your hybrid dial plan throughout Cisco to Teams migration projects. Its primary purpose is to guarantee that numbers are exclusively assigned on one platform, avoiding potential conflicts. In other words, ZPM and ZPC will ensure that your helpdesk never assigns a number that is already assigned in the other system.
You can also customize the feature to work with more complex hybrid dial plans. For example, users in CUCM who are transitioning from shorthand dial extensions (where the user’s number is the last X digits of their DID) to full e.164 numbers.