Phenol and m-cresol are common and refractory organic wastes in industrial wastewater. Anaerobic digestion is one of the most widespread technologies in dealing with this kind of wastewater. For the purpose of providing more useful information for the design and operation of the biodegradation trials of phenolic wastewater, two new modified Monod-type kinetics, the mutual inhibition between phenol and m-cresol, the co-metabolism between refractory substrates and easily degradable substrates were developed to simulate existing experimental data. Parameter K and parameters of mutual inhibition I are introduced to successfully present the promoting impact and mutual inhibition, respectively. The results of the simulations reproduce well the experimental data and therefore the developed model was validated. Based on the experimental data and model predictions from this study, it can be concluded that m-cresol affects the degradation of phenols and that the present of an easily biodegradable compound accelerates phenol degradation. The developed model can be used as a useful tool by the treatment plant operators in order to design optimal operation conditions for phenol degradation.