Part of the glycosylphosphatidylinositol-N- acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol and participates in the first step of GPI biosynthesis. {ECO:0000269|PubMed:16162815, ECO:0000269|PubMed:9463366}. This is the function of PIGH (phosphatidylinositol glycan anchor biosynthesis class H, ENSG00000100564).