HI Lance

If this buffer was made by mixing different volumes of  K2HPO4 (1M) & KH2PO4 (1M) then just add more of the former which will raise the pH

see table in the following link http://www.unl.edu/cahoonlab/phosphate%20buffer.pdf

Good luck 

Hi Lance,

If you don't mind having slightly more K in your solution then you can use KOH.

By adding KOH·xH2O to the initial buffer solution at pH = 6.2, until 7.5 is reached, the buffer would be slightly (or somewhat) diluted, since: KH2PO4 + KOH·xH2O → K2HPO4 + (x+1)H2O. It would be possible to correct this dilution effect, e.g., by evaporating some water by boiling, and later replenishing up to the original volume with water.   

If you don't object to a substantial increase in volume, you could add tribasic potassium phosphate solution at the same concentration as the pH 6.2 buffer. This will raise the pH without changing the phosphate concentration (it will increase the potassium concentration, however).

Na2HPO4 and NaH2PO4 both 1M conc mixture will give 7.2 pH. then from Hasselback Henderson equation you can adjust the pH.

HI Lance

If this buffer was made by mixing different volumes of  K2HPO4 (1M) & KH2PO4 (1M) then just add more of the former which will raise the pH

see table in the following link http://www.unl.edu/cahoonlab/phosphate%20buffer.pdf

Good luck