Why is phenolpthalein used as the indicator for the assay of tartaric acid?

Phenolphthalein is used as an indicator during the titration of tartaric acid because the pH at which phenolphthalein changes color (around pH 8.2-10) is close to the equivalence point of the titration of tartaric acid with a strong base like NaOH. This makes it a suitable indicator for detecting the endpoint of the titration when the acid has been completely neutralized by the base.