In phenol, the lone pair of electron present on oxygen is in conjugation with the ring, this leads to a partial double bond character that make it's bond length shorter

Introduction:
The bond length between carbon and oxygen in organic compounds can vary depending on the specific molecule and its structure. In the case of phenol and methanol, the carbon-oxygen bond length in phenol is slightly less than that in methanol. This difference can be attributed to several factors related to the electronic and steric effects in these molecules.

Electronic Effects:
Resonance:
Phenol has a resonance structure due to the delocalization of electrons in the benzene ring. This delocalization leads to a partial double bond character between the carbon and oxygen atoms, resulting in a shorter bond length. Methanol, on the other hand, lacks this resonance structure, leading to a longer bond length.

Inductive Effect:
Phenol also exhibits an inductive effect due to the presence of the electron-donating hydroxyl group (-OH). This effect causes electron density to be pulled towards the oxygen atom, resulting in a shorter carbon-oxygen bond length. In methanol, the absence of such an electron-donating group leads to a longer bond length.

Steric Effects:
Ortho Substitution:
In phenol, the ortho position to the hydroxyl group can be substituted with other groups. This substitution can cause steric hindrance, forcing the carbon-oxygen bond to become shorter. In contrast, methanol lacks such substitution possibilities, resulting in a longer bond length.

Conclusion:
In summary, the slightly shorter carbon-oxygen bond length in phenol compared to methanol can be attributed to the resonance and inductive effects caused by the hydroxyl group, as well as the steric effects arising from ortho substitution. These factors collectively contribute to the variation in bond length observed between these two organic compounds.