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 (PubMed:10481091). Required for biofilm production. The reaction proceeds via 2 processive phosphoryl transferase reactions; first from enzyme-phospho-Ser-108 to the substrate (generatinga 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 (PubMed:11716469, PubMed:16880541, PubMed:16595672, PubMed:22242625).