Acidity of any compound is generally directly proportional to its tendency to release H+ ions.
In case of any alcohol ( e.g. CH3-OH ), alkyl group attached to oxygen atom are of electron releasing nature due to+I inductive affect. This character of alkyl groups decreases oxygen 's electronegativity and hence its tendency to donate H+ get decreses.
In case of phenol, phenyl group attached to oxygen is of electron withdrawing nature due to -R resonance affect. This character of phenyl group increases the electronegativity of oxygen atom and hence its tendency to donate H+ increases.
Since phenol donate H+ ion easily than alcohols, phenols are more acidic than alcohols.