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 (MSH) biosynthesis pathway (By similarity). MSH and WhiB3 are probably part of a regulatory circuit that mediates gene expression upon acid stress (like that found in host macrophage phagosomes). MSH is one of the major redox buffers which protects bacteria against redox stressors and antibiotics; loss of MSH or ergothioneine (ERG, the other major redox buffer in this bacteria) leads to respiratory alterations and bioenergetic deficiencies that negatively impact virulence (By similarity). Note that is strain is avirulent (PubMed:18584054). 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. Belongs to the glycosyltransferase group 1 family. MshA subfamily.