Did My Blunder Cost Me the Job?

Dear Experts, I recently had a bit of an impromptu phone interview that I thought went very well, but as time went by I realized I'd made a huge blunder at the end of my interview that could've cost me my chance at a face-to-face interview. Despite following up to remedy my mistake and sending a separate thank-you email, I haven't heard back. I'd really like to know if my blunder actually was that big of a blunder, or if there was something else that didn't work, so I can improve my interview skills for next time. Is it okay to contact the person who interviewed me (an inside recruiter for the hiring company) to ask for feedback? Or is that just completely unreasonable? Our Twitter Advice Project (T.A.P.) is no longer an active campaign. To find an answer to the above question, please use the "Search" box in the right-hand column of this website.