Why was methyl red used as an indicator in this experiment rather than phenolphthalein?

Methyl Red, also called C. I. Acid Red 2, is an indicator dye that turns red in acidic solutions.

Phenolphthalein is a sensitive chemical with the formula C20H14O4 (often written as "HIn" in chemistry shorthand notation). Often used in titrations, it turns from colorless in acidic solutions to pink in basic solutions. If the concentration of indicator is particularly strong, it can appear purple. A phenolphtalein turns a bright orange color, in a solution containing a ph below 0.