Involved in the regulation of the phenol degradation pathway. Activates phenol hydroxylase expression in the presence of phenol. Activity is triggered by phenol binding. Homodimer. Constitutively expressed at a low level from a sigma70-type promoter. Contains an N-terminal signal reception (A) domain, followed by a hinge region (B domain), a transcription activation (C) domain and a C-terminal D domain. The A domain directly responds to external signals, the C domain contains the ATP-binding region that provides energy, and the D domain contains a helix-turn-helix DNA binding motif.