If you come across the phrase "era of error" and use it in your paper, you have to cite it.

The correct answer: True

If you come across the phrase "era of error" and use it in your paper, you have to cite it because obviously, it is a title of an existing literature. Your work will be tagged as a plagarized work plus you may get criminal charges for using a literature without acknowledging its existence under the intellectual rights act.

It doesn't take too much time to add some extra credits in your work anyway plus looking in another angle, your work will definitely look more compelling to read and it will seem factual. Unless the literature you cited is less credible.