The intracluster proton transfer reaction occuring in the hydrogen-bonded cluster cations of phenol (C₆H₅-OH) with water has been studied with trapped ion photodissociation (TIP) spectroscopy. Electronic spectra of [C₆H₅OH-(H₂O)_n]⁺ (n=1 - 4) were observed in the region 380 - 440 nm, which reveals the chromophore of the cluster ions. It was found that the cluster ions of n≤2 have the phenol ion (C₆H₅OH⁺) chromophore, while the n≥3 cluster ions exhibit the phenoxy radical (C₆H₅) chromophore, demonstrating that n=3 is the critical size for intracluster proton transfer. Chromophore switching, occuring in the cluster ions of phenol with other solvent molecules as well as water, was discussed on the basis of the proton affinity of the solvent species. It was concluded that the intracluster proton transfer is a "push ans pull" reaction determined only by the difference in the proton affinity between the phenoxy radical and the solvent molecules.