Converts the D-glycero-beta-D-manno-heptose 1,7-bisphosphate (beta-HBP) intermediate into D-glycero-beta-D-manno-heptose 1-phosphate by removing the phosphate group at the C-7 position. D-glycero-beta-D-manno-heptose 1,7-bisphosphate + H2O = D-glycero-beta-D-manno-heptose 1-phosphate + phosphate kcat is 22 sec(-1) and 5.9 sec(-1) with beta-HBP and alpha-HBP as substrate, respectively. Thus, the enzyme displays 150-fold more efficiency towards the beta- than the alpha-anomer (PubMed:20050615). Nucleotide-sugar biosynthesis; ADP-L-glycero-beta-D-manno-heptose biosynthesis; ADP-L-glycero-beta-D-manno-heptose from D-glycero-beta-D-manno-heptose 7-phosphate: step 2/4. Bacterial outer membrane biogenesis; LPS core biosynthesis. Monomer. Belongs to the GmhB family.