Guess what? When a prospective employer schedules a phone interview with you, you are supposed to answer the phone at the scheduled time. You are not supposed to call back half an hour later sounding like you just woke up and ask if you can do it now, as we had two recent candidates do.
If for some reason you miss a scheduled phone interview, the only correct response is to contact the employer immediately and express your extreme mortification. You must apologize profusely, and ideally you must offer an understandable excuse. ("A meeting with my boss ran over" is reasonable; "I wrote down the wrong time" is not.)
From the moment you make contact with the company, you are being evaluated. The "interview" isn't just the hour you might spend being asked questions; it's every email you send, every contact you handle, the way you treat the assistant, how prompt you are to respond when you're called about scheduling an interview -- it's all of it. Throw up red flags at any of those stages and you will either be out of the running or at least facing serious skepticism.