Answer. A salt formed by the total replacement of ionizable H+ ions of an acid by a positive metal ion is called neutral salt. Although H3PO4 is a weak acid, but as its all ionizable H+ ions has been replaced by sodium metal it is called neutral salt.
H3PO4(aq) + 3NaOH(aq) ———> Na3PO4(aq) + 3H2O(1)