The phrase "am source strength" does not have any direct antonyms. However, we can look at the individual words in the phrase to determine possible antonyms. "Am" is the first person singular form of the verb "be" and its antonym is "am not" or "are not". "Source" means origin or beginning, and its antonyms could be "end" or "finish". "Strength" refers to power or ability, and its antonyms could be "weakness" or "vulnerability". Therefore, we could say that the antonyms for "am source strength" could be "am not end weakness" or "are not finish vulnerability".