The hydrogen abstraction reaction PH3 + H --> PH2 + H-2 has been studied using an ab initio direct dynamic method. The optimized geometries and frequencies were calculated at the UQCISD/6-311+G** level for the reactant, products, and transition state, as well as 12 points along the minimum energy path. In order to obtain more reliable energies, the single-point calculations were carried out at the G2//QCISD level. The potential barriers obtained for the forward and reverse reactions are 3.24 and 25.99 kcal/mol, respectively. Reaction rate constants and activation energies were calculated for the temperature range 200-1600 K by the canonical variational transition state theory incorporating a small-curvature tunneling correction, and they are in satisfactory agreement with the available experimental values over the measured temperature ranges.