A quantitative model of the migrational history of any free water in the martian satellite Phobos is presented. Results include predicted depths of retained ice and current water fluxes as a function of latitude, regolith porosity and effective pore size. It is found that, despite Probos' small size, low albedo and proximity to the sun, ice may be present within the sounding depth of the GRUNT experiment on the Soviet Phobos Mission-at least at mid to high latitudes. Implications for other experiments on the Phobos mission are also discussed. ¿ American Geophysical Union 1989