Answer
This is an acid-base reaction.
Acid: $H_3PO_4$
Base: $NaOH$
Work Step by Step
An acid-base reaction follows the pattern:
$Acid + Base --\gt Salt + Water$
In this case:
$Acid = H_3PO_4$
$Base = NaOH$
$Salt = NaH_2PO_4$
$Water = H_2O$