Final answer:
The phrase indicating Mr. Auld's prohibition on Mrs. Auld teaching Frederick Douglass to read best supports the significance of literacy in Douglass's life, highlighting the obstacles he faced and the power literacy held.
Step-by-step explanation:
In answering Part B of the question related to the Narrative of the Life of Frederick Douglass, the phrase that best supports the idea of why literacy was so important to Douglass can be found in the excerpt where Mr. Auld forbids Mrs. Auld from teaching him to read. The exact quote from the text is: "Just at this point of my progress, Mr. Auld found out what was going on, and at once forbade Mrs. Auld to instruct me further, telling her, among other things, that it was unlawful, as well as unsafe, to teach a slave to read." This quote is pivotal because it not only reveals the barriers Douglass faced in his quest for literacy but also underscores the perception that educating slaves was considered dangerous by slaveholders, as literacy was a pathway to freedom and empowerment for the enslaved.