Phobos is .006 times the diameter of the Moon. [see page for the Moon]
Phobos is 1.78 times the diameter of Deimos (a satellite of Mars).
Phobos is .767 times the diameter of Telesto (a satellite of Saturn).
Phobos is .687 times the diameter of Helene (a satellite of Saturn).
Phobos is .253 times the diameter of Pandora (a satellite of Saturn).
Phobos is .119 times the diameter of Janus (a satellite of Saturn).
Phobos is .057 times the diameter of Mimas (a satellite of Saturn).
Phobos is .045 times the diameter of Enceladus (a satellite of Saturn).