Specifically catalyzes the cleavage of the D-lactyl ether substituent of MurNAc 6-phosphate, producing GlcNAc 6-phosphate and D-lactate. H2O + N-acetyl-D-muramate 6-phosphate = (R)-lactate + N-acetyl-D-glucosamine 6-phosphate Amino-sugar metabolism; N-acetylmuramate degradation. Homodimer. A lyase-type mechanism (elimination/hydration) is suggested for the cleavage of the lactyl ether bond of MurNAc 6-phosphate, with the formation of an alpha,beta-unsaturated aldehyde intermediate with (E)-stereochemistry, followed by the syn addition of water to give product. Belongs to the GCKR-like family. MurNAc-6-P etherase subfamily.