Plant roots rely on inorganic orthophosphate (Pi) transporters to acquire soluble Pi from soil solutions that exists at micromolar levels in natural ecosystems. Here, we functionally characterized a rice (<i>Oryza sativa</i>) Pi transporter, Os Phosphate Transporter-1;3 (OsPHT1;3), that mediates Pi uptake, translocation, and remobilization. <i>OsPHT1</i>;<i>3</i> was directly regulated by Os Phosphate Starvation Response-2 and, in response to Pi starvation, showed enhanced expression in young leaf blades and shoot basal regions and even more so in roots and old leaf blades. OsPHT1;3 was able to complement a yeast mutant strain defective in five Pi transporters and mediate Pi influx in <i>Xenopus laevis</i> oocytes. Overexpression of <i>OsPHT1</i>;<i>3</i> led to increased Pi concentration both in roots and shoots. However, unlike that reported for other known OsPHT1 members that facilitate Pi uptake at relatively higher Pi levels, mutation of <i>OsPHT1</i>;<i>3</i> impaired Pi uptake and root-to-shoot Pi translocation only when external Pi concentration was below 5 μm Moreover, in basal nodes, the expression of <i>OsPHT1</i>;<i>3</i> was restricted to the phloem of regular vascular bundles and enlarged vascular bundles. An isotope labeling experiment with <sup>32</sup>P showed that <i>ospht1</i>;<i>3</i> mutant lines were impaired in remobilization of Pi from source to sink leaves. Furthermore, overexpression and mutation of <i>OsPHT1</i>;<i>3</i> led to reciprocal alteration in the expression of <i>OsPHT1</i>;<i>2</i> and several other <i>OsPHT1</i> genes. Yeast-two-hybrid, bimolecular fluorescence complementation, and coimmunoprecipitation assays all demonstrated a physical interaction between OsPHT1;3 and OsPHT1;2. Taken together, our results indicate that OsPHT1;3 acts as a crucial factor for Pi acquisition, root-to-shoot Pi translocation, and redistribution of phosphorus in plants growing in environments with extremely low Pi levels.