> so they created a less potent alternative, phenylephrine,

Just to be clear, phenylephrine is not a “creation” or necessarily less potent. It’s an even older drug and a very effective vaso/venoconstrictor. The problem is it has poor oral absorption (bioavailability) as you note, so it doesn’t do much taken by mouth, but anything it does do is mostly deleterious. And thank god for that, because if it had the effect orally that it does via IV it would be killing a lot of people.