You just described me haha. In my Google phone screen, I fumbled around on solving an easy-moderate problem - so much so that when it ended, I felt that there was no way even I would hire me. And once it ended, I wrote the code for it in probably 10 minutes. Also, arranging it so that it was the first in the loop did not help either. The only good thing about the process was that the recruiter was nice about the whole debacle and did not make me feel too embarrassed.