This image from NASA's Mars rover Curiosity provides a comparison for how big the moons of Mars appear to be, as seen from the surface of Mars, in relation to the size that Earth's moon appears to be when seen from the surface of Earth.
This view of the two moons of Mars comes from a set of images taken by NASA's Mars rover Curiosity as the larger moon, Phobos, passed in front of the smaller one, Deimos, from Curiosity's perspective, on Aug. 1, 2013.
This image shows Phobos, the larger of Mars' two moons, as it transits in front of the sun. This image was taken by NASA's Mars Exploration Rover Opportunity during the afternoon of the rover's 3,078th Martian day, or sol.
The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter took two images of the larger of Mars' two moons, Phobos, within 10 minutes of each other on March 23, 2008. This is the first.