This is mostly hitting on supplemental phosphates. Apparently, the kind that come naturally are not fully absorbed, while additive forms are nearly completely absorbed and also are in amounts that can be high.
This is what I found to help understand phosphate:
Phosphate Additives in Food—a Health Risk
https://pmc.ncbi.nlm.nih.gov/articles/PMC3278747/pdf/Dtsch_Arztebl_Int-109-0049.pdf
Phosphates in higher than 700 mg a day amounts appear to cause abnormal aging.
Page four of the PDF describes amounts of natural vs. added phosphate sources, which helps you determine what to curb or have more of.
bkmk