https://doi.org/10.1351/goldbook.P04553
PH3 and compounds derived from it by substituting one, two or three hydrogen atoms by hydrocarbyl groups R3P. RPH2, R2PH and R3P (R ≠ H) are called primary, secondary and tertiary phosphines, respectively. A specific phosphine is preferably named as a substituted phosphane, e.g. CH3PH2 methylphosphane.
See:
phosphanes