The dynamics of submicron-sized dielectric particles lost from the Martian moon Phobos are studied in connection with the possible detection of dust by the Phobos 2 spacecraft. The motion of these small dust grains is influenced not only by gravity but also by solar radiation pressure and electromagnetic forces. The plasma environment of Mars is described by applying a hybrid gasdynamic-cometary model. Some of the submicron-sized grains ejected at speeds on the order of a few tens meters per second can stay in orbit around Mars for several months forming a nonuniform and time-dependent dust halo. The lifetime of the particles depends on their size, on the actual interplanetary parameters (constant or varying with a periodicity of 28 days) and also on the orbital position of Mars at the time of ejection since there is a 24¿ obliquity between the orbit of Phobos and that of Mars. ¿American Geophysical Union 1991