Infrared (IR) and Raman spectroscopies involving ionization detection mehods were applied for observing OH vibrations of size-selected phenol clusters. Also IR spectra of size-selected phenol cluster cations were observed by using IR multiphoton dissociation spectroscopy combined with an ion trapping technique. The cyclic form of the neutral phenol trimer was confirmed with experimental evidences. In the trimer cation, on the other hand, the IR spectrum shows that the cyclic form is no longer stable, but a chain form is feasible, in which all the phenyl moieties are bound by a single chain of hydrogen bonds. The drastic structure change induced upon ionization of the neutral trimer is discussed.