Phenol, when it first reacts with concentrated sulphuric acid and then with concentrated nitric acid, gives
Source: AIEEE 2008
Sulphonation blocks the para position and reduces the reactivity of the phenolic group against !!HNO_3!! and hence !!NO_2!! is attached to the ortho position. Also, because we have a very strong acidic medium, desulphonation takes place as well.