The –OH group in phenol is directly attached to the sp²hybridized carbon atom of the benzene ring. The carbon-oxygen bond length in phenol is smaller as compared to the carbon-oxygen bond length in alkyl alcohol and this is due to the partial double bond character or due to the resonance and charge distribution in phenol. Therefore, the OH group in phenols is more strongly held as compared to OH group in alcohols.

The resonance structures in phenol: