The function of IP6K3 (inositol hexakisphosphate kinase 3, ENSG00000161896) is as follows. Kinase that converts inositol hexakisphosphate (InsP6) to diphosphoinositol pentakisphosphate (InsP7/PP-InsP5)(PubMed:11502751, PubMed:34381031). Regulates cellular phosphate export by binding to the SPX domain of the XPR1 phosphate transporter (PubMed:34381031). {ECO:0000250|UniProtKB:Q8BWD2, ECO:0000269|PubMed:11502751, ECO:0000269|PubMed:34381031}.