They're not concerned with how you look, they only want to make sure you're great on the phone. I was hired on the spot after a phone interview. I had bright purple and pink hair and they referred to it as my "personal brand".

I applied online and a recruiter contacted me to schedule a phone interview. The interview consisted of about 4 behavioral questions. At the end of the interview I was offered the job. I found out later that they only do a phone interview for these positions because they wanted to see if you can build rapport over the phone. So be sure to be friendly.