Wiktionary
phenol red
n. A pH indicator and red dye used to test kidney function.
Wikipedia
Phenol red
Phenol red (also known as phenolsulfonphthalein or PSP) is a pH indicator frequently used in cell biology laboratories.
Usage examples of "phenol red".
The usual pH indicator in tissue culture media is phenol red, which turns clear in acid.
You took the buccal swab and swirled it around in a test tube containing a solution that turns acid in the presence of even a microgram of DNA, then added a drop of phenol red.