Hi Kenneth,
You can set the following search base for LDAP user search base under
System - LDAP - LDAP directory - LDAP user serach base.
dc=domain,dc=com;&(objectclass=user)
or
ou=test,dc=domain,dc=com;&(objectclass=user)
and make sure you map the Phone number field of CUCM with the "ipPhone" attribute of LDAP under "User fields to be syncronised"
the above worked for me once while testing.