You can add that field yourself, that's why Turba sources are configurable.

If you add a contact to a Nokia phone and enter only contact name and 
telephone number without any additional telephone number information 
(eg. mobile, home, work) then this telephone number information is 
silently discarded when phone is synced with turba using the default 
configuration with localsql.

There should be a data field in localsql configuration that matches 
telephone number without additional information, so that information 
is not lost during syncml sync session.

Example data from syncml session:
BEGIN:VCARD
VERSION:2.1
N:Example,User;;;
TEL:+1234
X-CLASS:PUBLIC
X-CATEGORIES:
END:VCARD