Amazon Developer interview questions

I uploaded my resume on their website and got an email within a week to schedule an interview. Due to personal reasons, I had to reschedule a couple of times. Then on the day of the interview, I got a call exactly at the scheduled time. Interview was fine, but the interviewer was not clear with the questions himself. This got me a bit irritated.

Was called by Amazon's recruiter after she had seen my resume on a jobs site. Set up a phone interview 4 days later. The hiring manager was friendly and polite. Wanted to help me out. But I screwed up the interview. After reading the reviews here, these were very simple questions, but I'm not too good in algorithms and am afraid that my extensive experience in OO design and architecture gets short shifted in this type of an interview. I expect that people with strong Math background would do really well. Anyway the questions asked were 1. Write the program to return a list of specified prime numbers. 2. Given two strings, determine if the two words are anagrams. 3. Compute the Big O of the solution. Now, at least the first two seem simple (even if using just a brute-force algorithm), but while doing this on the phone with syntactically correct code, it was not easy. I have about 20 years of enterprise application development. I think perhaps they need to have different type of phone interviews based on the background. But I guess it's one way to evaluate the thought process and given that this is Amazon, I guess algorithmic efficiency is probably in line with the scale. Note that though I have selected that this was a difficult interview, it's primarily my own inadequacy in dealing with algorithmic questions.