FGF23 and hyperphosphatemia: Teleological interpretations are always difficult to make and are often prone to error, but the principal physiological function of FGF23 may be to prevent hyperphosphatemia by increasing renal phosphate excretion and by indirectly reducing intestinal phosphate absorption through suppression of 1,25(OH)2D production, whereas that of PTH may be to counteract hypocalcemia.