Consulting a general science encyclopedia or chemical dictionary is a good first step. Total phosphate is most likely the sum of these two groups. To check, find another source of information about phosphates. Water is often tested for phosphate concentration, and so a book on water analysis might contain information about phosphates. Now it seems that total phosphate includes three groupings.
Further reading tells how to determine each type of phosphate.
Total phosphate can be determined by destroying the organic matter by oxidation and then hydrolyzing the condensed phosphates to orthophosphate. Dissolved orthophosphate is the form of phosphate that can be determined quantitatively by spectrophotometry. Other sources of background information on phosphate and water analysis may be found by searching in OBIS or other on-line catalog. Several of our scientific encyclopedias give no clue. We should consult the Library of Congress Subject Headings List and try again.