The article comes
so close to explaining a way to make it work, likely due to his hesitancy to recommend exceeding the recommended dose:
> Why is oral phenylephrine so useless? It is extensively metabolized, starting in the gut wall. You can find a bioavailability figure of 38% in the literature, but that appears to be the most optimistic number possible, and you can also find studies that show 1% or less. Overall, the Cmax is highly variable patient-to-patient, and the lack of cardiovascular effects at low doses argues for very low systemic effects (and expected low efficacy as a decongestant). The bioavailability increases at higher doses as you apparently saturate out some of the metabolic pathways, but at the 10mg dose typically used for decongestants, you can forget it.
Phenylephrine has variable Bioavailability. The bioavailability doubles if you take it with Tylenol, which is actually common in the context of colds. (Source: https://pubmed.ncbi.nlm.nih.gov/25475358/ ) The maximum dose was probably chosen based on worst-case scenarios, whereas the average person who complains it doesn't work is probably absorbing much less.
Always consult with your doctor, but I've found that taking a second dose of phenylephrine if the first one hasn't worked within about 30 minutes usually does the trick. Or just take it with Tylenol. It's worth checking your blood pressure to make sure you haven't started entering the realm of side significant side effects, though.
Also I should point out that pseudoephedrine isn't available behind the counter everywhere. It's prescription-only in some places.