In 1936 Heidegger started to write down his continuous remarks to his book Being and Time. At the very beginning he discussed the methodology of his research and the character of phenomenology in general.
Typically, he claimed that there never had been such a thing as phenomenology, for it was just a combination of Neo-Kantianism and psychologism. For Heidegger on the other hand, phenomenology represented a dynamism of thinking and a way of sharpening of philosophical insight.
But even such a conception of phenomenology is incapable to access and explicate the question of being as appropriate to itself. Therefore Heidegger abandons phenomenology, and "ontology" in favour of the so called "history of being".