Because extracellular phosphate stimulates FGF23 secretion from bone in vivo (Erben, 2017), it was previously believed that hyperphosphatemia triggers the augmented skeletal FGF23 secretion in CKD as part of an adaptive physiological response (Erben, 2017; Harjes et al., 2017). Here, FGF23 is linked to hyperphosphatemia.