Catalysis of the reaction: UDP-N-acetyl-D-glucosamine + phosphatidylinositol = UDP + N-acetyl-D-glucosaminylphosphatidylinositol.
UDP-N-acetyl-D-glucosamine:1-phosphatidyl-1D-myo-inositol 6-(N-acetyl-alpha-D-glucosaminyl)transferase activity