Structural isomers of isolated protonated phenol (C6H7O+) are characterized by infrared (IR) photodissociation spectroscopy of their weakly bound complexes with neutral ligands L (L = Ne, Ar, N-2). IR spectra Of C6H7O+-L recorded in the vicinity of the O-H and C-H stretch fundamentals carry unambiguous signatures of at least two C6H7O+ isomers: the identified protonation sites of phenol include the O atom (oxonium ion, O-C6H7O+) and the C atoms of the aromatic ring in the ortho and/or para position (carbenium ions, o/p-C6H7O+). In contrast, protonation at the meta and ipso positions is not observed. The most stable C6H7O+-L dimer structures feature intermolecular H-bonds between L and the OH groups of O-C6H7O+ and o/p-C6H7O+. Extrapolation to zero solvation interaction yields reliable experimental vibrational frequencies of bare O-C6H7O+ and o/p-C6H7O+. The interpretation of the C6H7O+-L spectra, as well as the extrapolated monomer frequencies, is supported by B3LYP and MP2 calculations using the 6-311G-(2df,2pd) basis. The spectroscopic and theoretical results elucidate the effect of protonation on the structural properties of phenol and provide a sensitive probe of the activating and ortho/para directing nature of the OH group observed in electrophilic aromatic substitution reactions.