The first product of glycogenolysis is:

Glycogenolysis, the breakdown of glycogen to release glucose, is an impoant pathway in energy use and reactions that utilize carbohydrates. Glycogenolysis involves three steps. First, the repetitive removal of glucose residues by phosphorylase breaking bonds between carbons 1 and 4, producing a glucose-1-phosphate molecule. However, this process stops when four glucose residues are left before the carbons 1 and 6 branch points. Second, a glucan transferase enzyme moves three residues to the linear pa of the glycogen chain, leaving only the final branched glucose residue. Third, a debranching enzyme cleaves the carbons 1 and 6 bond. A final enzyme conves the resulting glucose-1-phosphate molecules into glucose-6-phosphate for entry into glycolysis. Ref: Janson L.W., Tischler M.E. (2012). Chapter 6. Carbohydrate Metabolism. In L.W. Janson, M.E. Tischler (Eds), The Big Picture: Medical Biochemistry.