Peptidase that cleaves SIBLING (small integrin-binding ligand, N-linked glycoprotein)-derived ASARM peptides, thus regulating their biological activity (PubMed:15664000, PubMed:18162525, PubMed:18597632, PubMed:9593714). Cleaves ASARM peptides between Ser and Glu or Asp residues (PubMed:18597632). Regulates osteogenic cell differentiation and bone mineralization through the cleavage of the MEPE-derived ASARM peptide (PubMed:18597632). Promotes dentin mineralization and renal phosphate reabsorption by cleaving DMP1- and MEPE-derived ASARM peptides (PubMed:18162525, PubMed:18597632). Inhibits the cleavage of MEPE by CTSB/cathepsin B thus preventing MEPE degradation (PubMed:12220505). {ECO:0000250|UniProtKB:P70669, ECO:0000269|PubMed:12220505, ECO:0000269|PubMed:18162525, ECO:0000269|PubMed:18597632}. This is the function of Ensembl gene identifier ENSG00000102174 (PHEX, phosphate regulating endopeptidase X-linked).