18-Electron nucleophilic, Schrock-type phosphinidene complexes 3 [Cp*(Xy-N C)Ir PAr] (Ar = Mes*, Dmp, Mes) are capable of unprecedented [1 + 2]-cycloadditions with 1 equiv of isocyanide RNC (R = Xy, Ph) to give novel inclaphosphirane complexes [Cp*(Xy-N C)IrPArC=NR]. Their structures were ascertained by X-ray diffraction. Density functional theory investigations on model structures revealed that the iridaphosphirane complexes are formed from the addition of the isocyanicle to 16-electron species [Cp*Ir=PAr] forming first complex 3 that subsequently reacts with another isocyanicle to give the products following a different pathway than its nitrogen analogue [Cp*Ir Nt-Bu] 1.