I also am unable to backup the Address Book without getting an error.
Please post the exact error message here otherwise it is very difficult to help.
You can set the sync of the address book to go from the Blackberry to Outlook. On the user properties, under PIM Sync, under the Address Book heading, choose "Device to Server" (standard is "Bidirectional").
Nevertheless, the mobile number of a contact should always sync, so something else might be wrong in your setup. You should probably check the PIM Sync field mappings.