Abstract: The composite 20%Co₃O₄/Bi₂Fe₄O₉ (20%Co/BFO) was prepared via a combination of coprecipitation and calcination methods. Subsequently, 20%Co/BFO was immobilized onto the surface of honeycomb cordierite (HC) support through an impregnation approach to fabricate the 20%Co/BFO@HC monolithic catalyst. Characterization including XRD, FTIR, and SEM confirmed the successful preparation of 20%Co/BFO and 20%Co/BFO@HC. A monolithic reactor based on 20%Co/BFO@HC was then constructed and applied for the catalytic activation of peroxymonosulfate (PMS) to degrade phenol wastewater. The effects of variables including 20%Co/BFO loading, PMS dosage, initial phenol concentration, initial pH, and wastewater flow on the degradation of phenol in the monolithic reactor were systematically investigated. Under the optimal operating conditions of the reactor (20%Co/BFO loading: 95.7 mg; PMS concentration: 1.25 mmol/L; phenol concentration: 40 mg/L; pH: 6.39; wastewater flow: 1 L/min), the phenol degradation efficiency reaches 96.95%. Cyclic experiments were also conducted in the monolithic reactor. After five consecutive degradation cycles, the phenol removal efficiency of the 20%Co/BFO@HC-PMS system remained as high as 93.84%, demonstrating the excellent stability of the prepared 20%Co/BFO@HC. In addition, radical quenching experiments verified the presence of 4 reactive oxygen species (ROS) during phenol degradation, namely SO₄^•−、^•OH、O₂^•− and ¹O₂. The contribution of these ROS to the oxidative degradation of phenol was ranked in the descending order of O₂^•−>¹O₂>^•OH>SO₄^•−. Finally, the chemical oxygen demand (COD) of the phenol wastewater before and after the catalytic reaction was measured. The calculated COD removal efficiency reached 86.61%, indicating that the monolithic reactor based on the 20%Co/BFO@HC-PMS system exhibits superior mineralization for phenol wastewater.