Phenol can be oxidized to the end products when oxygen is used as an electron acceptor. This study evaluated phenol oxidation in an oxygen-based membrane biofilm reactor (MBfR). The system achieved highest oxidation of both phenol and glucose when the phenol loading and glucose loading was ∼4.7 and ∼55 g m−2 day−1, respectively. These conditions were sufficient to prove an O2 flux of at least 46 g O2 m−2 day−1. In the case of feeding solely with phenol, the MBfR accomplished the highest phenol oxidation (∼100%) when the phenol loading was about 5.6 ± 0.9 g m−2 day−1 and the O2 flux was higher than 13.4 ± 2.2 g O2 m−2 day−1. However, higher phenol loading could be compensated by a higher O2 pressure, and the best performance occurred when the phenol loading was 5.6 g m−2 day−1, the O2 pressure was ∼0.54 atm, and hydraulic retention time was 2.5 h. Membrane fouling caused a reduced O2 flux, which led to low phenol-oxidation efficiency. However, the bacterial population present in MBfR was analyzed by PCR-denaturing gradient gel electrophoresis and a low biodiversity was found.