Catalyzes the phosphorolysis of beta-1,4-mannooligosaccharides to mannose 1-phosphate (Man1P) and shorter mannooligosaccharides. Can also catalyze the phosphorolysis of 4-O-beta-D-mannopyranosyl-D-glucopyranose (Man-Glc), but shows higher activity toward longer mannooligosaccharides. Involved in a mannan catabolic pathway which feeds into glycolysis. [(1->4)-beta-D-mannosyl](n) + phosphate = [(1->4)-beta-D-mannosyl](n-1) + alpha-D-mannose 1-phosphate kcat is 20.7 sec(-1) for Man-Glc. kcat is 7.06 sec(-1) for beta-1,4-mannobiose. kcat is 27.5 sec(-1) for beta-1,4-mannotriose. kcat is 33.1 sec(-1) for beta-1,4-mannotetraose. kcat is 31.9 sec(-1) for beta-1,4-mannopentaose. Optimum pH is 6.5. Optimum temperature is 45 degrees Celsius. Homohexamer in solution. Both RaMP1 (Rumal_0852) and RaMP2 catalyze the phosphorolysis of a beta-1,4-mannosidic linkage at the non-reducing end of a substrate, but acceptor specificities are clearly different. Belongs to the glycosyl hydrolase 130 family.