Salt analysis of Ag salts

According to Firsching [1],

silver phosphate is indeed soluble in ammoniacal solution due to formation of silver-ammonia complex.

The following is the solubility data of $ce{Ag3PO4}$ in $ce{NH4OH}$ at $pu{35.5 °C}$ presented by Saraswat [2]:

begin{array}{rr} hline c(ce{NH4OH})/ & c(ce{Ag3PO4})/ \ pu{mmol l^-1} & pu{mmol l^-1} \ hline 0 & 0 \ 4.05 & 0.133 \ 8.09 & 0.265 \ 16.18 & 0.531 \ 32.36 & 1.061 \ 64.72 & 2.057 \ 129.45 & 4.113 \ 258.90 & 8.292 \ 517.80 & 26.478 \ hline end{array}

References

1. Firsching, F. H. Precipitation of Silver Phosphate from Homogenous Solution. Anal. Chem. 1961, 33 (7), 873–874. DOI: 10.1021/ac60175a018.
2. Saraswat, H. C. Formula of Complex Compounds from Solubility Data. Proc. Indian Acad. Sci. (Math. Sci.) 1949, 30 (6), 329–332. DOI: 10.1007/BF03048752.