Catalyzes the addition of sulfite to phosphoenolpyruvate (PEP) to yield (2R)-phospho-3-sulfolactate (PSL). (2R)-O-phospho-3-sulfolactate = H(+) + phosphoenolpyruvate + sulfite Cofactor biosynthesis; coenzyme M biosynthesis; sulfoacetaldehyde from phosphoenolpyruvate and sulfite: step 1/4. In Xanthobacter strain Py2 coenzyme M plays a role in epoxide carboxylation by serving as the nucleophile for epoxide ring opening and the carrier of the C3 unit that is ultimately carboxylated to acetoacetate. Belongs to the phosphosulfolactate synthase family.