Catalyzes the reversible 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:235429, PubMed:11786017, PubMed:21672603, PubMed:30337572). Acts on 6-amino and 6-oxopurines including deoxyinosine, deoxyguanosine, deoxyadenosine, adenosine, guanosine, and inosine (PubMed:235429, PubMed:11786017, PubMed:21672603, PubMed:30337572). Does not act on xanthosine (Probable). May also catalyze a phosphate-dependent transfer of the pentose moiety from one purine base to another (PubMed:235429). a purine D-ribonucleoside + phosphate = a purine nucleobase + alpha-D-ribose 1-phosphate a purine 2'-deoxy-D-ribonucleoside + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate + a purine nucleobase inosine + phosphate = alpha-D-ribose 1-phosphate + hypoxanthine adenosine + phosphate = adenine + alpha-D-ribose 1-phosphate guanosine + phosphate = alpha-D-ribose 1-phosphate + guanine 2'-deoxyadenosine + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate + adenine 2'-deoxyguanosine + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate + guanine 2'-deoxyinosine + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate + hypoxanthine Optimum pH is 7.1 for deoxyinosine as substrate (PubMed:235429). Optimum pH is 7.5 for inosine as substrate (PubMed:235429). Optimum pH is 8.2 for hypoxanthine as substrate (PubMed:235429). Homohexamer; trimer of homodimers. Belongs to the PNP/UDP phosphorylase family.