We present visible and thermal infrared observations of the Martian surface acquired during three Phobos transits. Observations show a decrease of up to ∼20% of the reflected solar energy, consistent with the fraction of the Sun disk eclipsed by Phobos, and no measurable surface cooling. Thermal modeling indicates that the top millimeter of the regolith has a thermal inertia larger than 100 J m−2 K−1 s−1/2 regardless of the surface morphology, and is consistent with TES regional thermal inertia values derived from diurnal cycles (e.g. ∼200 J m−2 K−1 s−1/2). The thermophysical properties of the top millimeter of the regolith exclude the presence of widespread thermally-thick dust layers, are consistent with those of the diurnal skin depths at TES and THEMIS spatial resolutions, are in accordance with high-resolution images of the surface showing no surface mantling, with General Circulation Model results, thermally derived rock abundance values, albedo, and spectroscopic data.