Sodium-phosphate symporter which seems to play a fundamental housekeeping role in phosphate transport by absorbing phosphate from interstitial fluid for normal cellular functions such as cellular metabolism, signal transduction, and nucleic acid and lipid synthesis. In vitro, sodium-dependent phosphate uptake is not significantly affected by acidic and alkaline conditions, however sodium-independent phosphate uptake occurs at acidic conditions. May play a role in extracellular matrix and cartilage calcification as well as in vascular calcification. Functions as a retroviral receptor (By similarity). Homodimer. Widely expressed with highest levels in liver, heart and brain. Belongs to the inorganic phosphate transporter (PiT) (TC 2.A.20) family.