Phenol is less acidic than ______________.

The presence of electron-withdrawing group(e.g. nitro group), enhances the acidic strength of phenol.

It is due to the effective delocalization of negative charge in phenoxide ion. This makes the OH bond weaker.

If an electron releasing group (example alkoxy group) is present it makes the O-H bond stronger.

Thus H⁺ ion can be easily removed.