As part of the purine salvage pathway, catalyzes the phosphorolytic breakdown of the N-glycosidic bond in the beta-(deoxy)ribonucleoside molecules, with the formation of the corresponding free purine bases and pentose-1-phosphate (PubMed:17918964). Preferentially acts on 2'-deoxyinosine and inosine, and to a lesser extent on 2'-deoxyguanosine and guanosine (PubMed:17918964). Has no activity towards adenosine or 2'-deoxyadenosine (PubMed:17918964). inosine + phosphate = alpha-D-ribose 1-phosphate + hypoxanthine guanosine + phosphate = alpha-D-ribose 1-phosphate + guanine 2'-deoxyguanosine + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate + guanine 2'-deoxyinosine + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate + hypoxanthine Inhibited by 5'-deaza-1'-aza-2c-deoxy-1'-(9-methylene) immucillin-H (DADMe-ImmH). kcat is 41 sec(-1) with inosine as substrate (PubMed:17918964). kcat is 1 sec(-1) with guanosine as substrate (PubMed:17918964). kcat is 54 sec(-1) with 2-deoxyinosine as substrate (PubMed:17918964). kcat is 5.4 sec(-1) with 2-deoxyguanosine as substrate (PubMed:17918964). Purine metabolism; purine nucleoside salvage. Homotrimer. Belongs to the PNP/MTAP phosphorylase family.