Pseudoephedrine and Phenylephedrine… What’s the Difference?

I know one is regular Sudafed and the other is Sudafed PE and I know pseudo can be made into meth and so far phenyl can’t, but why? They are both ephedrine based. No I’m not a cook, just curiousity.
Good answers, but I was looking more for the differences in chemical bonds.

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