Herein, we propose a novel post-modification synthesis strategy to prepare M-doped (M = Fe, Co, Mo, etc.) transition metal phosphides (TMPs) composed of Co and MoP embedded in nitrogen-doped carbon nanospheres (denoted as Co–Mo–P@NCNS-600). Through engineering of the anion chemistry of cobaltosic oxide nanoparticles to adjust the composition, morphology and crystallographic orientation of the Mo-based metal–organic frameworks (MOFs), and then a pyrolysis–phosphidation process, the Co–Mo–P@NCNS-600 electrocatalyst exhibits excellent electrocatalytic performance (overpotentials (η₁₀) of 270 mV for the oxygen evolution reaction and 62 mV for the hydrogen evolution reaction), benefiting from the well-designed structure and the electronic state control. Furthermore, when the Co–Mo–P@NCNS-600 is used in a water-splitting device, it can reach a 10 mA cm⁻² current density at low potential (1.58 V), and exhibits excellent stability for 380 000 s (105.6 h). Density functional theory (DFT) results indicate that the successful construction of the Co–Mo–P active site will effectively modulate the intrinsic electronic properties and improve the electrochemical performance.