Ksp = [Ag+]3[PO43-]
Silver nitrate and sodium phosphate react to form silver phosphate and sodium nitrate. The balanced equation is 3 AgNO3(aq) + Na3PO4(aq) equals Ag3PO4(s) + 3 NaNO3(aq).
Neither - it is a saltAdded:But when dissolved (not much, but still 0.01 mmol) it splits into ions of which phosphate (PO43-) is quite strongly basic, pH about 10