Phenolphthalein is a synthetic indicator with a working $pH$ range of approximately $8.3$ to $10.0$ (transition from colorless to pink).

• In a titration between a Weak Acid (e.g., Acetic acid) and a Strong Base (e.g., $NaOH$), the salt formed (Sodium acetate) undergoes basic hydrolysis.
• This means the $pH$ at the equivalence point is $>7$ (typically around $8.5-9$).
• Since this $pH$ falls perfectly within the phenolphthalein range, it is the ideal choice for this titration.