Diiminophenyl (dimph) proved to be an excellent ligand platform to stabilise a low-valent phosphorus centre. The resultant compound dimphP (3), which can be rationalized as an imino-stabilised phosphinidene or benzoazaphosphole, shows remarkable chemical stability: it withstands treatment with water and oxidizers (O₂ and pyridine oxide) and only reacts with excess strong acid (e.g. HCl) to generate the P(III) chloride (dimHph)PCl (7), where dimHph stands for a diiminophenyl group hydrogenated at one imine position. Surprisingly, substitution of the chloride under some nucleophilic (KOBu^t) and electrophilic conditions (Me₃SiOTf) regenerates the parent compound 3, by proton removal from the weakly acidic CH₂N position. A related species (dimH₂ph)P (14), where dimH₂ph stands for diiminophenyl hydrogenated to imino(aminomethyl)phenyl, is produced upon thermal rearrangement of the hydride (dimHph)PH (13). X-ray structures of compounds 3, 14, and (dimHph)PO₂CH (17) are also discussed.