Contact glow discharge electrolysis (CGDE) or plasma electrolysis technology is a proven effective method for degrading such kind of wastewater because it can produce •OH, H•, and other active species in large quantities responsible for breaking down phenol structure. This study aims to obtain high-efficiency phenol degradation using an injection of air directly through the anode. This research investigated the effect of the voltage to the current connections in CGDE in order to estimate the possibilities for an optimum electrical power on the phenol degradation. In this research, the production of hydrogen peroxide, the percentage of phenol degradation, and specific energy were used as the main research indicators. Experimental results show that each electrical power (500, 600, 700 watt) has an optimal value for the percentage of degradation. The optimal condition was found at 700 watt with the rate of air injection of 0.2 L/min. After the first 45 minutes, the phenol degradation was valued at 79.5%. Under the same conditions, with an addition of air injection, the phenol degradation shot up to 93.22%. Experimental results show that the largest phenol degradation was obtained at 99.48% after 90 minutes during the experiment. This research clarified that air injection on plasma anode could improve process efficiency.