a 1,2-diacyl-sn-glycero-3-phospho-[alpha-D-6-acyl-mannopyranosyl-(1<->6)-D-myo-inositol] + GDP-alpha-D-mannose = a 2-O-(alpha-D-mannosyl)-6-O-(6-O-acyl-alpha-D-mannosyl)-1-phosphatidyl-1D-myo-inositol + GDP + H(+) — reaction