AIPMT 2010 Physics and Chemistry Paper

Presence of electron withdrawing substituent increases the acidity while electron releasing substituent, when present, decreases the acidity.
Phenyl is an electron withdrawing substituent while −CH3 is an electron releasing substituent. Moreover, phenoxide ion is more resonance stabilised as compared to benzyloxide ion, thus releases proton more easily. That's why is a strong acid among the given.