One can filter Contacts using the content of text fields in a contact, but cannot filter by a phone # or part of a phone #. It has happened to me on quite a few occasions that I have a visitor phone # but the name does not match an existing contact. Would love to be able to filter by the phone #, or part of it, dropping all non-numeric characters (parens, dashes, spaces, periods, etc.) before trying to match the phone # or part of phone #.