I googled the phrase, and only got an essay on Stumpf, one I cannot read and which does not include the phrase in the freely available content.
I then looked at the SEP article for Stumpf, whom I had at least forgotten of the existence of.
extension and color form a concrete whole which can only be separated through abstraction. From this point of view, the concept of space, as any concept, draws upon its origin in sense perception and is, to use the Scholastic expression, an abstracta cum fundamento in re [abstraction with a basis in reality].
For Stumpf, do these "abstractions" exist, and can there be a phenomenology of them? How does Stumpf use 'phenomenology without phenomena'? Can there be a phenomenology, a study that uses the phenomenological method, into anything that is not phenomenal? According to either Stumpf or Husserl.