A phosphate group is also called a phosphate and delivers the phosphate to ATP, AMP and AdP. As proteins go through the phosphorylation process, it becomes a covalently attached phosphate group. All of the phosophodiester linkages that join nucleotides together in polynucleic acids are phosophate groups as well. In general terms, if you see the letter "P" in a biomolecule, it means that it is a phosphate group.
Phosphate serves a useful function within animal cells, buffering substances that can possibly enter the cells and cause problems. Phosphate cells like NaH2PO4 and Na2HPO4 commonly go into buffering solutions for the pH levels inside cells, just like potassium salts.
Within biological systems, one of the most important places where phosphates appear is the structural element inside teeth and bones. Both of these are made of calcium phosphate in a crystalline shape, taking on the form of hydroxyapatite. The tough enamel that exists on mammalian teeth is made of fluoroapatite, which is a phosphate made of hydroxy calcium, in which fluoride ions have replaced some of the hydroxyl groups.
Plants bring in phosphorus through a number of pathways, such as the direct uptake and arbuscular mycorrhizal pathways. In the mineral realm, phosphates are the most frequently found form of phosphorus.