B) He wants to communicate directly with the readers.
Explanation:
From the given options, the sentence that best explains why Walt Whitman uses such a simple phrase as "who I am or what I mean" in the given quotation from "Song of Myself" is the corresponding to option B: He wants to communicate directly with the readers, that is why he uses a simple phrase and also he addresses the reader in a direct way by using the pronoun "you."
