Phosphate loading is legal.

It is nothing to do with pregnancy. The result is "positive" for phosphate, meaning, presumably, that higher levels of phosphate then normal are being found in the blood. Phosphate is a normal substance in foods which is needed in the body mainly as a constituent of bone. Excess phosphate is normally filtered out of the blood by the kidneys and ends up in the urine. A positive serum phosphate test, which I assume means higher than the normal level, is usually indicative of the kidneys not functioning as efficiently as they used to.

Phosphates are commonly used in fertilizers.

histones

The compound with formula Na3PO4 is named "sodium phosphate", "trisodium phosphate", "sodium ortho-phosphate", or "trisodium ortho-phosphate".