Transfers mannose from GDP-mannose to dolichol monophosphate to form dolichol phosphate mannose (Dol-P-Man) which is the mannosyl donor in pathways leading to N-glycosylation, glycosyl phosphatidylinositol membrane anchoring, and O-mannosylation of proteins. a dolichyl phosphate + GDP-alpha-D-mannose = a dolichyl beta-D-mannosyl phosphate + GDP For the phosphorylated protein, the Vmax increases to 146.7 nmol/min/mg enzyme, whereas the KM stays at 1.1 uM for GDP-mannose, increasing the catalytic efficiency 6-fold. Protein modification; protein glycosylation. Interacts with the C-terminus of SAC1, thereby sequestering it to the endoplasmic reticulum in exponentially growing cells. Under nutrient limitation conditions, this interaction is rapidly abolished. Present with 1885 molecules/cell in log phase SD medium. Belongs to the glycosyltransferase 2 family.