The function of FGF23 (fibroblast growth factor 23, ENSG00000118972) is as follows. Regulator of phosphate homeostasis (PubMed:11062477). Inhibits renal tubular phosphate transport by reducing SLC34A1 levels (PubMed:11409890). Up-regulates EGR1 expression in the presence of KL (By similarity). Acts directly on the parathyroid to decrease PTH secretion (By similarity). Regulator of vitamin-D metabolism (PubMed:15040831). Negatively regulates osteoblast differentiation and matrix mineralization (PubMed:18282132). {ECO:0000250|UniProtKB:Q8VI82, ECO:0000269|PubMed:11062477, ECO:0000269|PubMed:11409890, ECO:0000269|PubMed:15040831, ECO:0000269|PubMed:16597617, ECO:0000269|PubMed:18282132}.