Zimbra GAL entries are viewed by clients as Zimbra contact objects. You can define which LDAP attributes map to which contact attributes. As long as the LDAP attributes are mapped to the correct contact fields, everything should work. There are some more details here:
GAL Attribute Mapping - Zimbra :: Wiki
If you do a GAL search from the Zimbra Web Client, do you the other fields display (phone, address, etc)?