Exploiting high-efficient and stable non-precious metal-based electrocatalysts toward hydrogen evolution reaction (HER) is of enormous significance to address the shortage of global power source, but there remain major challenges. Here we present a facile and controllable strategy to synthesize a strongly coupled ultrasmall-cobalt phosphide/nitrogen-doped graphitic carbon (u-CoP@NC) hybrid structure via phosphorization from a porous coordination polymer (PCP) precursor. The PCP-derived u-CoP@NC exhibits remarkable activity and stability for HER, achieving a current density of 10 mA cm⁻² with a low overpotential of 131 mV in acidic media and 111 mV in basic media. The corresponding Tafel slopes present in acidic and basic media are 62.7 and 70.3 mV dec⁻¹, respectively. Results reveal that the enhanced electrocatalytic performance of u-CoP@NC originates from the strongly coupled u-CoP nanoparticles and graphitic carbon layer, and the perfect dispersity of the active sites. This research opens up new avenues for designing earth-abundant metal-based electrocatalysts with high capability for water splitting applications.