Highly reversible phosphoryltransferase. The phosphomannomutase activity produces a precursor for alginate polymerization, the alginate layer causes a mucoid phenotype and provides a protective barrier against host immune defenses and antibiotics. Also involved in core lipopolysaccaride (LPS) biosynthesis due to its phosphoglucomutase activity. Essential for rhamnolipid production, an exoproduct correlated with pathogenicity. Required for biofilm production. The reaction proceeds via 2 processive phosphoryl transferase reactions; first from enzyme-phospho-Ser-108 to the substrate (generating a bisphosphorylated substrate intermediate and a dephosphorylated enzyme), a 180 degree rotation of the intermediate (probably aided by movement of domain 4), and subsequent transfer of phosphate back to the enzyme. alpha-D-mannose 1-phosphate = D-mannose 6-phosphate alpha-D-glucose 1-phosphate = alpha-D-glucose 6-phosphate Binds 1 Mg(2+) ion per subunit. Nucleotide-sugar biosynthesis; GDP-alpha-D-mannose biosynthesis; alpha-D-mannose 1-phosphate from D-fructose 6-phosphate: step 2/2. Bacterial outer membrane biogenesis; lipopolysaccharide biosynthesis. Monomer. Belongs to the phosphohexose mutase family. Extended N-terminus.