Catalyzes the reversible decarboxylation of 4-hydroxybenzoate. 4-hydroxybenzoate + H(+) = CO2 + phenol The enzyme activity is enhanced by Mg(2+), Fe(2+), Mn(2+) and Ca(2+). No stimulation is observed with Cu(2+) and Zn(2+). Optimum pH is 7.5. Optimum temperature is 30 degrees Celsius. It loses above 50% decarboxylase activity at 40 degrees Celsius for 5 minutes, and above 25% enzyme activity remains after incubation at 50 degrees Celsius for 5 minutes. Component of the decarboxylase complex composed of the subunits B and C (Potential). The subunit D usually found in other organisms seems to be absent. Belongs to the UbiD family.