You cannot associate empty attribute values. If you edit an attribute and the attribute is not associated with any value, the edited attribute does not appear in the contact browser

If you edit the phone attributes and update the phone number for a contact, and want POM to recalculate the time zone associated with the phone number, you must empty the existing time zone value in the respective time zone attribute. To update the country code attribute, you must empty the existing country code value in the respective country code attribute.

If the phone number or the email id of any contact already exists in the DNC list, you can edit all other attributes of that contact except the phone number and the email id.