Transition metal phosphides (TMPs) have emerged as promising non-precious electrocatalysts for the oxygen evolution reaction (OER), offering tunable composition and high intrinsic conductivity. Under OER conditions, however, TMP surfaces tend to in situ oxidize into metal oxyhydroxides, which act as the true active species for water oxidation. This self-transformation boosts catalytic activity but also highlights challenges: the newly formed oxides/hydroxides can be structurally unstable and less conductive than the parent phosphide, undermining long-term performance. To address these issues, researchers employ strategic nanoengineering from core–shell architectures that stabilize active phases, to heteroatom doping and interface engineering that enhance conductivity and modulate electronic structure. These designs improve OER activity and durability by mitigating phase instability and electron transport losses. Advanced in situ spectroscopic characterizations and theoretical modeling (e.g., density functional theory (DFT)) play a crucial role in unraveling TMPs’ dynamic reconstruction and guiding the development of next-generation OER catalysts.