Highly unlikely it’s calcium phosphate. The chemistry of phosphate precipitation would require high pH, high CH and high phosphate levels. Phosphates are rarely greater than 3-5ppm in the worst case and so the chemistry would require a CH in the thousands of ppm to precipitate phosphates.
If it’s calcium carbonate it will “fizz” vigorously in MA. If it’s calcium sulfate, it will slowly dissolve in concentrated MA. Calcium phosphate will remain mostly undissolved even in concentrated MA. If you can capture these precipitates and acid test them, it will tell you a lot.