Usually in titrations involving amines as the titrator or titrant. Phenolpthalein changes colour at around pH 9 which is commonly the pH at which an amine neutralises. You usually use it when you...
There are a lot of indicators around. Choosing which one to use depends on what you're analyzing for, what pH the endpoint happens at, what kind of reaction is happening in the flask, etc. Some...
Litmus paper, or other pH papers can measure pH. Many pH test papers can measure specific pH values. There are also instruments called pH meters that can measure pH.