The carbon-oxygen bond in phenol is slightly stronger than that in methanol because of two reasons:

i) Due to the resonance, it develops apartial double bond character in carbon-oxygen bond. Thus, decrease in the size of carbon-oxygen bond in phenol.

ii) In phenol, Oxygen is directly attached to a sp²hybridized carbon atom, whereas in methanol, Oxygen is directly attached to a sp³ hybridized carbon atom. Thus, the bond formed between oxygen and sp² hybridized carbon atom is slightly stronger than that in methanol.