I only know one person who has ever found phenylephrine effective. It's definitely not for me, but they've done single-blinded self-studies (with help) to see if it's a placebo effect, and it's pretty clearly not.

DXM is also not a placebo, although it might be specifically for cough.

I don't especially want the FDA to ban them, but requiring separating out the acetaminophen might not be the worst idea.