Catalyzes the last step of the phosphorylated serine biosynthetic pathway, i.e. dephosphorylation of O-phospho-L-serine to form L-serine. Is also able to dephosphorylate O-phospho-D-serine with similar efficiency. Displays a poor activity on L-phosphothreonine, and cannot use L-phosphotyrosine, pyridoxal phosphate, glucose 6-phosphate, or fructose 6-phosphate as substrates. H2O + O-phospho-L-serine = L-serine + phosphate H2O + O-phospho-D-serine = D-serine + phosphate kcat is 1506 sec(-1) (at pH 7.0 and 70 degrees Celsius) for the dephosphorylation of O-phospho-L-serine. Amino-acid biosynthesis; L-serine biosynthesis; L-serine from 3-phospho-D-glycerate: step 3/3. Homodimer. Cells lacking this gene show serine auxotrophy when grown in a synthetic MP medium, in contrast to wild type. Addition of L-serine to the medium restores growth of the deletion mutant. Belongs to the HAD-like hydrolase superfamily.