As a result of rapid industrialization and population development, toxic chemicals have been introduced into water systems in recent decades. Because of its excellent efficiency and simple design, the three-dimensional (3D) electro-Fenton method has been used for the treatment of wastewater. The goal of the current study is to explore the efficiency of phenol removal by the 3D electro-Fenton process, which is one of the advanced oxidation processes (AOPs). In the present work, the effect of the addition of granular activated carbon (GAC) particles to the electro-Fenton system as the third electrode would be investigated in the presence of graphite as the anode and nickel foam as the cathode, which is the source of electro-generated hydrogen peroxide (H2O2). The influence of operation parameters (current density, electrolysis time, and GAC) on catalytic performance will be studied, which will be adjusted by the response surface methodology (RSM). The pH was adjusted to 3, and the airflow was set to 10 L/h. According to the results the nickel foam was an excellent cathode material choice. The best conditions for phenol elimination were at current density of 3.56 mA/cm2, FeSO4.7H2O dosage of 0.1 mM, GAC of 30g, and a time of 3 h to attain the removal rates of phenol and chemical oxygen demand (COD) of 98.79% and 93.01%, respectively. The results showed that time had a higher effect on the phenol and COD removal efficiency, while the impact of current density was lower. The model equation's high R2 value (97.90%) demonstrates its suitability.