The acidic nature of phenol is due to the formation of stable phenoxide ion in solution C6H5OH + H2O ⇄
C6H5O−
Phenoxide‌ion
+H3O+ The phenoxide ion is stable due to resonance
The negative charge is delocalized in the benzene ring which is a stabilizing factor in the phenoxide ion and increase acidity of phenol. whereas no resonance is possible in alkoxide ions (RO–) derived from alcohol. The negative charge is localized on oxygen atom. Thus, alcohols are not acidic.