Phenomenon, Illusion, Will

What, in the World as Will and Representation, begin as Kantian 'phenomena', e. g. physical bodies, end as 'illusions'.  In contrast, at B69 of the 1st Critique, Kant clearly denies that "these objects are mere illusions."  He then proceeds, at B70, to diagnose the fundamental target of his entire Critical enterprise: "it is only when we ascribe objective reality to [subjective representations], that it becomes impossible for us to prevent everything from being transformed into mere illusion."  But, ascribing objective reality to a subjective representation is precisely and plainly what Schopenhauer does when what he first discovers as "I will", in #42 of the Fourfold Root of the Principle of Sufficient Reason, becomes impersonal 'Will' in WWR.  Hence, what, from a Kantian perspective, is illusory in Schopenhauer's system, is its purported noumenon, not its phenomena.