Measurement of an organism's, organ's, tissue's or cell's capacity to respond, such as by a change in activity, state or condition, to phenylephrine (PE), the phenylethanolamine with IUPAC name (R)-3-[-1-hydroxy-2-(methylamino)ethyl]phenol and formula C9H13NO2 that acts as a selective alpha1-adrenergic receptor agonist, decongestant and vasoconstrictor.