why the respiratory pathway consider an amphibolic pathway rather than as a catabolic pathway

An amphibolic pathway is the one which is involved in both, breakdown (catabolism) and synthesis of  substrates (anabolism). During respiratory pathway, a number of things are broken down into simpler products to derive energy from them. For example, glucose is broken down by glycolysis to form pyruvate which is further processed to give ATP. But apart from these  catabolic processes, a number of intermediates of the Kreb's  cycle of the respiratory pathway are involved in synthesis of other compounds, like fatty acid synthesis. So, both catabolic and anabolic processes occur during the respiratory pathway hence it is considered as an amphibolic pathway.