H3PO4 is a weak acid so it will donate H+.
F– is a weak base (anions will accept H+).
Since there is no strong acid or strong base, the reaction must be an equilibrium:
H3PO4(aq) + F–(aq) → ← HF(aq) + H2PO4–(aq)
Acid: H3PO4
Base: F–
Conjugate Acid: HF
Conjugate Base: H2PO4–