Involved in actively transporting phosphate into cells via Na(+) cotransport in the renal brush border membrane (PubMed:12690469, PubMed:16113079). The cotransport has a Na(+):Pi stoichiometry of 2:1 and is electroneutral (PubMed:16113079). 2 Na(+)(out) + phosphate(out) = 2 Na(+)(in) + phosphate(in) Optimum pH is 7.5. Localized at the brush border membrane in the kidney. Expressed only in the kidney. Belongs to the SLC34A transporter family.