Involved in the biosynthesis of the compatible solute mannosylglucosylglycerate through a phosphorylating pathway. Catalyzes the transfer of the glucose moiety from a nuleotide sugar such as UDP-alpha-D-glucose to the position 2 of 3-phospho-D-glycerate (3-PGA) to form glucosyl-3-phosphoglycerate (GPG). UDP-glucose is the preferred substrate, but it can be partially replaced by ADP-glucose. (2R)-3-phosphoglycerate + an NDP-alpha-D-glucose = (2R)-2-O-(alpha-D-glucopyranosyl)-3-phospho-glycerate + a ribonucleoside 5'-diphosphate + H(+) (2R)-3-phosphoglycerate + UDP-alpha-D-glucose = (2R)-2-O-(alpha-D-glucopyranosyl)-3-phospho-glycerate + H(+) + UDP (2R)-3-phosphoglycerate + ADP-alpha-D-glucose = (2R)-2-O-(alpha-D-glucopyranosyl)-3-phospho-glycerate + ADP + H(+) Requires divalent cations for activity. Inhibited by ADP and EDTA. Optimum pH is 7.0 (at 60 degrees Celsius). Optimum temperature is 70 degrees Celsius. Homodimer in solution. Belongs to the glycosyltransferase 2 family.