The numerical phase function calculated with Mie theory is discussed in this paper. 1) The comparison between Mie phase function and Henyey-Greenstein phase function is made. Results show that Mie phase function is of great advantage, specially, in the simulation of polarized light transport in turbid medium. 2) The equivalent phase function of phantom consisting of micro-spheres of different sizes is presented. With this discussion, the differences between numerical phase function, Henyey-Greenstein phase function, and experimental measured phase function are discussed.