Positive regulator of sigma-B activity. Dephosphorylates RsbV in response to energy stress. H2O + O-phospho-L-serine = L-serine + phosphate H2O + O-phospho-D-serine = D-serine + phosphate Induced by entry into stationary phase, but not by carbon and energy starvation. The PAS domain may participate in sensing the overall energy level of the cell and communicate this information to the phosphatase domain.