Returns one phone number exactly as stored, without the renaming and type conversion the list endpoint applies — enabled and destination_record come back here as strings that may be null, not booleans. Per-number access grants are not checked. destination_hold_music comes back as a sound reference (an object such as {"type": "recording", "id": "…"}), or null when not set, in the same form a create or update takes. An id that matches no number answers 404.