Phosphorylates glucosylglycerol-phosphate the precursor of the osmoprotectant glucosylglycerol necessary for salt adaptation of Synechocystis. 2-O-(alpha-D-glucopyranosyl)-sn-glycerol 3-phosphate + H2O = 2-O-(alpha-D-glucopyranosyl)glycerol + phosphate Monomer. Interacts with GGPS. Belongs to the histidine acid phosphatase family.