Catalyzes the reversible phosphorylytic cleavage of uridine to uracil and ribose-1-phosphate which can then be utilized as carbon and energy sources or in the rescue of pyrimidine bases for nucleotide synthesis (PubMed:7488099). Shows broad substrate specificity and can also accept deoxyuridine and other analogous compounds (Probable). . This is the function of UPP1 (uridine phosphorylase 1, Ensembl gene identifier ENSG00000183696).