That is the hard problem, actually. If we could operationalize those terms, we would be able to study what they refer to with a reductionist lens. Until then, we're kind of stuck using words to point at experience rather than at structural definitions.

In case you're honestly not sure what everyone is talking about, though: There's a difference between red as a certain frequency of light and red as experienced. Yes, we know there's a strong connection between the two, and we can describe in some fair detail how a certain frequency of light stimulates optic nerves and is processed in the brain and so on. But it's not at all clear how we get from those mechanical processes to the experience of red. We don't experience red as a frequency; we experience it as red! That latter bit, the redness of red, is what people refer to as the qualium of red. ("Qualium" is the singular form of "qualia".)

The reductionist thesis maintains that there must be a way to reduce the connection between physical mechanisms and qualia down to mechanisms. The hard problem of consciousness is that no one seems to be able to come up with even an in-principle plausible way of making that connection. In other words, everyone is confused but doesn't have a clear way to even start dispelling the confusion. People like Daniel Dennett have made efforts, but many people question whether their efforts even count as progress.

So in short: "phenomenal consciousness" refers to the experience of qualia, although we don't know what that means aside from pointing at the fact that everyone seems to experience qualia and that mechanisms affect but don't seem to be qualia. "Subjective experience" usually refers to the same thing, but is often used to emphasize the fact that the experience of qualia seems to depend on the individual; e.g., you don't experience my experiencing red the way I do and vice versa.