Phobos-class frigates were a class of starship on active duty in Starfleet during at least the early 24th century. (Star Trek: Of Gods and Men) The Phobos-class design was similar to that of the Andorian-designed Loknar-class spaceframe. (FASA RPG: Federation Ship Recognition Manual) In appearance, the class had a saucer-shaped primary hull similar to that of the Constitution-class, albeit with twin warp nacelles mounted on pylons above the primary hull. The nacelles were apparently of the type LN-64 or similar.