Involved in actively transporting phosphate into cells via Na(+) cotransport. 3 Na(+)(out) + phosphate(out) = 3 Na(+)(in) + phosphate(in) Optimum pH is 6.0. Localized at the brush border membranes of enterocytes. Highly abundant in the ileum of small intestine, whereas it is almost absent in the duodenum and in the jejunum. Up-regulated in the entire small intestine by low-phosphate diet. Up-regulated by metabolic acidosis. Belongs to the SLC34A transporter family.