Full Idea
One of our first tasks will be to prove that if we posit an 'I' or subject as that which is proximally given, we shall completely miss the phenomenal content of Dasein.
Gist of Idea
If we posit 'I' as the starting point, we miss the mind's phenomenal content
Source
Martin Heidegger (Being and Time [1927], I.1.10)
Book Reference
Heidegger,Martin: 'Being and Time' [Blackwell 1962], p.72
A Reaction
Descartes had thrown doubt on the informativeness of the phenomena, so presumably your phenomenologist is not interested in whether they reveal any truth. So why are unreliable phenomena of any interest?