Equivalent weight stands for Molecular weight/N factor N factor means H+ or OH- exchange in case of acid and bases respectively and in case of salts it is charge on cation.
Molecular Mass of H3PO4 is 98gm.
In first reaction one OH- is exchanged so equivalent weight = 98÷1=98gm.
In second Reaction Two OH- are exchanged, so equivalent weight = 98÷2 = 49gm.
In third reaction three OH- ions is exchanged, so equivalent weight = 98÷3 = 32.666667gm.