OK, Let's isolate phenol* from the solution which contains it.
A basic aqueous solution contains the sodium salt* of phenol, sodium phenolate*.
You want to change sodium phenolate (salt of a weak organic acid) to the water-insoluble phenol (weak organic acid) by converting the salt to a protonated*, non-ionic* form.
Which solution will you add?
Organic Web Chem University of Alberta