Is it implausible to claim consciousness is a fundamental?
Not at all. Is phenomenological thinking plausible? Absolutely! And by extension, idealism itself is completely plausible and metaphysically robust. George Berkeley had subjective idealism. In fact, idealism went through a long historical period of being favored over materialism and was the popular metaphysical position in the German Idealist movement:
The most famous representatives of this movement are Kant, Fichte, Schelling, and Hegel. While there are important differences between these figures, they all share a commitment to idealism. Kant’s transcendental idealism was a modest philosophical doctrine about the difference between appearances and things in themselves, which claimed that the objects of human cognition are appearances and not things in themselves. Fichte, Schelling, and Hegel radicalized this view, transforming Kant’s transcendental idealism into absolute idealism, which holds that things in themselves are a contradiction in terms, because a thing must be an object of our consciousness if it is to be an object at all.
Thus, there are a number of positions that err on the side of the mental as foundational most famously Husserl and his phenomenology which was immensely influential to Continental philosophers. Here, consciousness is where the thinking begins, and then the thinker brackets his normal thoughts to "deconstruct" them by reasoning about appearances and actuality which could be thought of as a search for certainty in the face of the problem that naive realism presents, how do you know what is true and real?
There are three terms, naturalism, materialism, and physicalism that are often taken by contemporary thinkers to be synonymous because of an increasingly scientific worldview. But a careful reading of philosophy does not metaphysically necessarily expunge idealism and phenomenology. It's actually quite a radical stance to reject consciousness and phenomenological thinking. Even Daniel Dennett who identifies as a eliminative materialist nonetheless puts forth positions like intentional stance and heterophenomenology in order to cope with consciousness despite his claims it's an illusion (whatever that means).
So, it is certainly out of fashion not to be a physicalist and materialist, but as Chalmers suggests, even for analytic philosophy there is no escaping consciousness as a philosophical problem. Ultimately, there is always a looming conversation in philosophy regarding monism, dualism, or something else, and consciousness always plays prominently in the discussion.