Recall how phenylamine is diazotized below 1 degree C and the diazonium salt is warmed with water to form phenol.
Recall the reactions (reagents and conditions) by which phenol can be produced: reaction of phenylamine with HNO3 or NaNO3, and dilute acid below 1°C to produce the diazonium salt; further warming of the diazonium salt with H2O to give phenol.