My scenario is different, customer is trying to swap phones and says he sees the change in AD but not in MAS.
From the install guide:
Ensure telephony fields on the directory server and MiCollab database remain in sync, Data
mismatches that occur between telephony fields are not sent to the Managed Detained
Queue because they cannot be reconciled from MiCollab. The following telephony fields
are ignored during a synchronization update: Home Element, Mobile Phone Directory Number;
Primary Phone Directory Number and Secondary Phone Directory Number:
From reading this I wouldn't think you could swap an extension, hence my question