Why do hydrogen phosphate salts make basic solutions?

Aqueous solutions of hydrogen phosphate salts are basic because the hydrogen phosphate ion (${\text{HPO}}_4^{2-}$) acts more effectively as a base—defined as a proton acceptor—than as an acid in water.1

While orthophosphoric acid is a triprotic acid capable of donating three protons, its salts exhibit varying acidity or alkalinity depending on their specific ion composition. Specifically, the ${\text{HPO}}_4^{2-}$ ion has a greater tendency to accept a proton than to donate one, which results in a basic solution. In contrast, dihydrogen phosphate salts (${\text{H}}_2{\text{PO}}_4^{-}$) form weakly acidic solutions because the ion functions as a weak acid, while orthophosphate salts (${\text{PO}}_4^{3-}$) form strongly basic solutions because the orthophosphate ion is a moderately strong base.1