A telephone number as the source gave it, not normalized. Free-form text in any format: national (`(206) 555-0114`, `206.555.0114`), international (`+1 206 555 0167`, `+447700900013`), with punctuation or an extension (`512.555.0190 x39`). A source may use a filler number such as `0000000000` for a missing one; it identifies no one and is kept as given. Never empty or only spaces. Rules derive `e164_phone_number` only from a number written with its country code and a leading `+`: a national number has no E.164 form, and so no phone hash, because its country can't be known from the number.