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. Belongs to the phosphosulfolactate synthase family.