Theoretical and experimental studies on buried ion-exchanged waveguides using field-assisted annealing (FAA) in erbium-doped phosphate glasses were reported. The procedure for making buried waveguides using a two-step process was demonstrated. An analytical model for the FAA process was developed, and both the refractive index profiles and the effective buried depths of these waveguides are predicted. This model is based upon the available data derived from the ion-exchanged planar waveguide measurements. The mode intensity profiles as well as the buried depths were measured with the use of standard end-fire coupling setup and a calibrated image capture card. The buried depths are found to be in good agreement with the simulated results.