We present a theoretical study of the phase behavior of mixed brushes composed of charged and noncharged polymers that are mutually incompatible. We derive the self-consistent-field (SCF) equations from the canonical ensemble for a system of polyelectrolyte and uncharged polymers with added salt. Within the saddle point approximation, the modified Edwards Hamiltonian results in expressions for the chemical potential and species density fields in terms of the Green's function propagator and the nonlinear Poisson-Boltzmann equation for the electrostatic potential. These SCF equations were fully numerically analyzed to achieve results that are exact within the assumption of lateral mean field. The two-dimensional phase behavior of the mixed brushes ( assuming that the brushes are laterally mobile) was examined using the conventional free energy of mixing analysis. The predictions on the effects of such control variables as the charge content of the polyelectrolyte species, ionic strength of the medium, and the surface grafting density of the chains on the conformation properties and phase behavior of the mixed brushes are presented. The results suggest that an increase in the effective charge on the polyelectrolyte (through variation of either charge content or ionic strength) favors the mixed state, while increasing the grafting density favors phase separation.