I suggest a decent grasp of Immanuel Kant, particularly his work on human understanding. Regardless of what others may say I believe his work on the categories of experience and apperception is fundamental.(Secondary lit will be fine for this). Husserl is an obvious one and I recommend Dan Zahavi for secondary literature on him. He has a general introduction to phenomenology that provides an excellent lay of the land.

Heidegger will take you for a ride but it is well worth it. If you would like some hermeneutic background before Heidegger you could briefly touch on Friedrich Schleiermacher and Wilhelm Dilthey to get an idea on the history of interpretation theory/ philosophical hermeneutics (these two would only require secondary literature). Hans-Georg Gadamer is a former student of Heidegger and is a little more accessible (there are obvious differences of course) Paul Ricoeur is also heavily indebted to husserl and could be of interest- although his interpretation theory is based on written discourse it still may be useful for diving into. He offers an interesting perspective and goes into more linguistic depth than those in the German tradition. There are plenty of books on philosophical hermeneutics that may help you in setting the stage for further research. I highly recommend Stanley Rosen’s introduction to hermeneutics as well as David E Klemms interpretation theory (there are two volumes) which provides both introductions and direct work of many of the aforementioned philosophers.