A general theory is developed for the electrophoretic mobility of spherical soft particles (i.e., spherical hard colloidal particles of radius a coated with a layer of polyelectrolytes of thickness d) in concentrated suspensions in an electrolyte solution as a function of the particle volume fraction phi on the basis of Kuwabara's cell model. In the limit d --> 0, the mobility expression obtained tends to that for spherical hard particles in concentrated suspensions, whereas in the limit a --> 0, it becomes that for spherical polyelectrolytes (charged porous spheres with no particle core). Simple approximate analytic mobility expressions are derived for the case where relaxation effect is negligible. It is found that in practical cases, the phi dependence of the mobility is negligible for d much less than a, whereas for d much greater than a, the mobility strongly decreases with increasing phi.