That is not the point in this case. P-aminophenol does not drop out of solution. It is practically insoluble. It never gets into solution. Only that part that is combined with sodium from the hydroxide to form the phenolate gets into solution. If you start with a solution of p-aminophenol.HCl, the first hydroxide that hits the solution makes salt out of the HCl and precipitates the p-aminophenol. When that has been done, if there is more hydroxide available, the phenolate is formed. Whichever starting point you use, if there is not enough hydroxide to make phenolate out of all the p-aminophenol, some of it will remain undissolved. However, in the presence of sulfite, aerial oxidation will make monosulfonate and hydroxide which can act on precipitated p-aminophenol to make phenolate. But that is not the precipitated aminophenol changing the pH. That is a change in pH due to aerial oxidation unprecipitating some of the amnophenol.