Tertiary (3°) phosphines, with the formula RP,  are traditionally prepared by alkylation of phosphorus trichloride using Grignard reagents or related organolithium compounds:
:3RMgX  +  PCl    →   PR   +  3MgX
In the case of trimethylphosphine, triphenyl phosphite is used in place of the highly electrophilic PCl:
: 3 CHMgBr + P(OCH) → P(CH) + 3 CHOMgBr
Slightly more elaborate methods are employed for the preparation of unsymmetrical tertiary phosphines, with the formula RR'P.  The use of organophosphorus-based nucleophiles is typical.  For example, lithium diphenylphosphide is readily methylated with methyl iodide to give methyldiphenylphosphine:
:LiiP(CH) + CHI → CHP(CH) + LiI
Phosphine is a precursor to some tertiary phosphines by hydrophosphination of alkenes. For example, in the presence of basic catalysts PH adds of Michael acceptors such as acrylonitrile:
:PH + 3 CH=CHZ → P(CHCHZ) (Z = NO, CN, C(O)NH)
Tertiary phosphines of the type PRR′R″ are "P-chiral" and optically stable.
From the commercial perspective, the most important phosphine is triphenylphosphine, several million kilograms being produced annually. It is prepared from the reaction of chlorobenzene, PCl, and sodium.  Phosphines of a more specialized nature are usually prepared by other routes.