Your recipe looks strange to me because it is a mixed sodium and potassium buffer. Is this for a very specific application?
The two components to mix a phosphate buffer are normally used to adjust the desired pH of the final buffer. To do so you mix up the two buffers with equal molarity to the desired pH. The components to get a Sodium Phosphate buffer are Na2HPO4 and NaH2PO4 or K2HPO4 and KH2PO4 for a potassium Phosphate buffer, nut I have never seen a mix of both components.