I have a few phrases that have to be in Bold only when they are being uses in a a certain sentence.

In other worlds.

If the "mary had a little lamb" comes up it should be bold. but if the phrase comes up "the dish ran away with the spoon" that should be plain text.

Is there a way to make the style change to bold when having a certain phrase or answer and having it return to plain text style when that answer is not being used?

Try this:

Case(

PatternCount(Book Name ; "mary had a little lamb");

Substitute (Book Name ; "mary had a little lamb" ; TextStyleAdd ("mary had a little lamb" ; Bold ) );

TextStyleAdd (Book Name ; Plain ) )

sorry I forgot to change the field name. Book name is the field name with your phrase in it