Catalyzes the transfer of a N-acetyl-glucosamine moiety to 1D-myo-inositol 3-phosphate to produce 1D-myo-inositol 2-acetamido-2-deoxy-glucopyranoside 3-phosphate in the mycothiol biosynthesis pathway. 1D-myo-inositol 3-phosphate + UDP-N-acetyl-alpha-D-glucosamine = 1D-myo-inositol 2-acetamido-2-deoxy-alpha-D-glucopyranoside 3-phosphate + H(+) + UDP Homodimer. Transiently induced by thiol-oxidant diamide, under control of SigR. Also induced when mycothiol is oxidized or conjugated. Belongs to the glycosyltransferase group 1 family. MshA subfamily. Extended N-terminus.