Ab initio molecular orbital (MP2/6-311G(d,p) and CASPT2/ANO) and density functional theory (DFT/IGLO-III) calculations have been applied to determine some basic properties of phenylphosphinidene (C6H5P). Geometries, harmonic vibrational wavenumbers, singlet-triplet energy gaps, heats of formation and hyperfine splitting constants have been calculated. Phenylphosphinidene has a triplet (3)A(2) ground state lying 22 +/- 3 kcal/mol below the closed-shell singlet (1)A(1) state and some calculated properties are: heat of formation at 0 K Delta H-f,0(0) = 68 +/- 5 kcal/mol, vertical ionization energy IE(v) = 10.6 +/- 0.3 eV, electron affinity EA(a) = 0.89 +/- 0.3 eV, proton affinity PA = 140 +/- 5 kcal/mol and isotropic hyperfine splitting constant a(P-31) = 66 +/- 3 G. The open-shell singlet (1)A(2) State is also a low-lying state having comparable energy with the (1)A(1). The properties of C6H5P are similar to those of methylphosphinidene (CH3P). The singlet-triplet gap ((1)A'-(3)A(2)) in CH3P amounts to 26 +/- 3 kcal/mol. Relative to the CH3P, the phenyl group has a small effect on the singlet state but seems to destabilize the tripler state and thereby reduce the singlet-triplet gap.