The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the Mars Reconnaissance Orbiter, recorded at a resolution of about seven meters per pixel.
Diameter 22.2 km
18.8 mi.
Distance from primary 9,377 km
5,826 mi.

Phobos is the first moon of Mars. Discovered in August 18, 1877 by Asaph Hall.