We have used x-ray photoelectron and Raman spectroscopies to characterise the effect of the incorporation of F on the short range structure of Na-P-O and Na-Al-P-O glasses. The incorporation of F into NaPO3 depolymerises the glass structure by preferentially replacing bridging oxygen with chain terminating P-F bonds. The addition of AlF3 to NaPO3 modifies the phosphate network primarily by linking Al(O,F) polyhedra with P(O,F)4 tetrahedra. Remelting these latter glasses with NH4HF2 increases their F contents and depolymerises the structure through the formation of additional P-F and Al-F bonds at the expense of the bridging POAl bonds. Changes in glass properties are sensitive to these structural modifications.