Cobalt-based　phosphate/phosphonates　are　a　class　of　promising　water　oxidation　catalysts　at　neutral　pH.　Herein,　we　reported　a　facile　hydrothermal　synthesis　of　various　nanostructured　cobalt　phenylphosphonates.　It　is　found　that　the　number　of　hydroxyl　group　of　structure-directing　reagent　is　crucial　for　the　construction　of　3D　hierarchical　structures　including　hierarchical　nanosheet　flower-like　assemblies　and　nanothorn　microsphere.　These　samples　were　characterized　by　scanning　electron　microscopy,　transmission　electron　microscopy,　X-ray　diffraction,　infrared,　and　X-ray　photoelectron　spectroscopy　techniques.　They　can　act　as　highly　efficient　electrocatalysts　for　the　oxygen　evolution　reaction　at　neutral　pH.　Among　these,　hierarchical　cobalt　phenylphosphonate　nanothorn　flowers　present　excellent　performance,　affording　a　current　density　of　1　mA　cm−2　required　a　small　overpotential　of　393　mV.　This　work　offers　a　new　clue　to　develop　high-performance　metal　phosphonate/phosphate　catalysts　toward　electrochemical　water　oxidation.　©　2020　Dalian　Institute　of　Chemical　Physics,　the　Chinese　Academy　of　Sciences