In this study, a model for calculating the bidirectional scattering properties of phosphor layer was established by considering the light absorption and light conversion of phosphor particle simultaneously. Based on the present model, the light extraction efficiency was calculated and validated by comparing with the existing experimental data and models. It is demonstrated that the present model predicts better. The transmission and reflection intensities of blue light and yellow light were found to be the functions of phosphor thickness. There exists a close critical phosphor thickness for reflected blue light and transmitted yellow light. The critical phosphor thickness is relative to the phosphor concentration.