I'm sure this will be unpopular, but I think the real problem with Phenylephrine is that it isn't dosed appropriately in standard formulations.

The standard 10mg dose is too low. Decongestants work by constricting blood vessels, which inherently increases blood pressure as a side effect.

Pseudoephedrine at standard doses is known to raise blood pressure slightly. Phenylephrine at standard doses (10mg) shows no such effect (Source https://journals.lww.com/ebp/abstract/2018/03000/how_much_do... )

Phenylephrine does increase blood pressure when delivered by IV at doses that work. The oral 10mg dose just isn't enough to get absorbed and do anything.

It's not that phenylephrine is ineffective, it's that it's underdosed in the oral formulation.