I had read someone claim he was against foundationalism, or
specifically psychologism. Does he agree to use a limited amount or am
I wrong about this being an experience?
Although it may sound like Descarte relied on the 'seeming' (i.e: subjective experience) of there being an 'I'; his argument does not rely on it, in fact, it is build on something that goes deeper than the subjective experience itself.
In Meditations, He started by Cartesian Skepticism, that is, roughly speaking : Anything that can be otherwise, you can doubt.
Psychedelics, for example, can influence my brain and create hallucinations that look as if real, and many dreams look as if real, then : I reality can be doubted. Using this method, Descartes ruled out everything that is accessible through the senses in the first step.
The second step is to rule out logical, deductive and mathematical truths : It is possible for a demon to miss with my mind and make me think that 1+1=3, or that if P then Q, Q therefore P is valid, or that P and not-P can both be true...etc.
Then it should follow that everything in Logic and our different modes of reasoning can also be doubted.
What is left, if I doubt everything? I doubt.
Can I doubt that too? can I doubt that I (am there to) doubt? it should be obvious that this is impossible, it leads to a self-referential paradox, it cannot be true that I doubt that I doubt. So, I think (I doubt) therefore I am.
One of the objections to Descartes' Cogito comes from Bertrand Russell, it goes something like this : "The premise I think, should be translated to a proposition 'There is thought' " , for using 'I' in the premise to infer the conclusion is circular.
If it is possible, It would be interesting if you edit your question and add a link to the source that claims Descartes was against foundationalism.