Dipole moment of phenol is smaller than that of methanol. Why?

Dipole moment of phenol is smaller than that of methanol due to the electron withdrawing effect of the phenylring. Due to the resonance, the polarity of the C-O bond in phenol decreases.

In methanol, due to the presence of electron releasing methyl group, the electron density on the oxygen atom increases and thus, the C-O bond in methanol is more polar.