Google Autenticator for IPHONE
If your GW2 code was removed during the update of the authenticator app the only way to restore your account is to contact costumer support and descripe your problem. (Try to explain it with some more details…)
FYI: The google authenticator app on iphone (not android) deleted all codes during the update to v2.0 which is now removed from the appstore and will be put back if the bug is fixed. If you already got the update your codes are lost.