CardDAV
CalDAV's sibling for address books — syncing contacts between phone, computer and server over HTTP.
RFC 6352 (2011), also a WebDAV extension. Each contact is stored as a vCard file, and the protocol adds field search, shared address books and efficient syncing of only what changed.
Same ecosystem as CalDAV: Apple Contacts, Nextcloud, Fastmail, Thunderbird. That calendars and contacts got two separate standards rather than one is a characteristic IETF outcome — they solve related problems with the same underlying machinery but different data formats.