Involved in the biosynthesis of glucosylglycerate. Catalyzes the dephosphorylation of glucosyl-3-phosphoglycerate (GPG) and mannosyl-3-phosphoglycerate (MPG) to glucosylglycerate (GG) and mannosylglycerate (MG), respectively. (2R)-2-O-(alpha-D-glucopyranosyl)-3-phospho-glycerate + H2O = (2R)-2-O-(alpha-D-glucopyranosyl)-glycerate + phosphate 2-O-(alpha-D-mannosyl)-3-phosphoglycerate + H2O = (2R)-2-O-(alpha-D-mannosyl)-glycerate + phosphate Divalent cations in the following order of efficiency: cobalt, magnesium, and, to a lesser extent, nickel ions. Optimum pH is between 5.5 and 6.5 with GPG and MPG as substrates. Optimum temperature is 50 degrees Celsius with GPG and 60 degrees Celsius with MPG. With GPG as substrate, the activity becomes undetectable below 20 degrees Celsius and above 70 degrees Celsius, and with MPG as substrate, the activity is almost undetectable at 30 degrees Celsius. At 50 degrees Celsius, divalent cations are absolutely required for GpgP activity with GPG and MPG as the substrates. Monomer. Belongs to the HAD-like hydrolase superfamily. MPGP family.