Maybe it is just semantics then. If the thing-in-itself is “what is there” for real (the ontic) and the phenomena is only whatever we can experience of that thing via our senses ("thing-as-it-appears’), then we could say the thing-in-itself becomes Christ, and only the phenomena remain. Even with just this semantic difference though, it seems more intuitive to my mind. This would be on the “dual aspect” view where the noumenon is the intelligible understanding of the thing-in-itself or “thing-as-thought.”
If we draw a distinction between the thing-in-itself from the phenomenon (subjective) and noumenon (objective), it might seem like consubstantiation. I think there is a subtle but crucial difference. The thing-in-itself of the bread and wine exists before and after consecration; but the noumena of the bread and wine is replaced by the noumena of Christ. What is objectively there in the Eucharist is the thing-in-itself of Christ, body, blood, soul and divinity (the Real Presence). The thing-in-itself of the bread and wine is not objectively there as noumena, only its phenomena remains and our subjective experience of it.
The latter “dual object” view seems much more intuitive to me, because the appearance of bread and wine has some sort of reality, obviously. It retains the physical properties, and it can nourish and intoxicate us. To say this is all accident with no substance is true, I don’t doubt that, but it seems like saying that we are experiencing something when we are not, which is counter-intuitive. How do we account for our experience? With Kant, we can say that there is a real experience of bread and wine, but it’s phenomenal and subjective only. What we are really consuming, objectively, if we could know what is really there as a thing-in-itself, is Christ.
Full disclosure: I was raised Lutheran, and its sacramental theology (admitting of course that it does not actually have valid sacraments) has traditionally been described — and condemned — as consubstantiation. It doesn’t work philosophically because a thing cannot be two things at the same time, but it has the advantage of offering an intuitive reason for the experience of bread and wine. Also, I wouldn’t want to use Immanuel Kant here in a way that would commit us to the rest of his philosophy.