Phosphorus is an important mineral as it is a vital component of structures such as DNA, RNA, and bone and plays a key role in cellular processes such as ATP generation and cell signaling. It is ubiquitously found in many of the food items consumed by us. Activated vitamin D3 plays a key role in enhancing absorption in the gut. Serum phosphorus is mainly regulated by renal excretion. Nearly 80–85% of filtered phosphate is reabsorbed in renal tubules via phosphate transporters. Hormones such as parathyroid hormone, fibroblast growth factor 23 (FGF 23) enhance phosphorus excretion. Hypophosphatemia can occur due to inadequate absorption from the gut or due to excess loss through the kidneys as in hypophosphatemic rickets or renal transporter defects. Hyperphosphatemia occurs due to excess release from cells such as in crush injuries or rhabdomyolysis or due to inadequate excretion such as with hypoparathyroidism or renal failure. Hypophosphatemia is treated with phosphorus supplements along with calcitriol to enhance absorption. Recently, FGF 23 antibodies have been a breakthrough treatment for FGF 23-mediated hypophosphatemic conditions. Hyperphosphatemia is treated acutely with hydration and by using phosphate binders to reduce absorption in the gut.