A phone interview is usually granted to candidates who are unable to travel to the interview. Usually these candidates are from outside California, or have difficulty financially to come to Berkeley. Phone interviews are also offered to candidates who have very high stats, and the interview scoring may not be a huge factor into that candidates acceptance. Again, this is based on what Ive heard and I do not work in the admissions office so I cannot be certain.
I believe the in-person interview would be more favorable because you have the opportunity to visit the school, take a tour of the schools, speak to other students and your possible future classmates, and youll definitely receive more attention compared to a phone interview.
There is only one interview date usually near the beginning of the year. They probably will start inviting candidates for an interview near the end of December or January. Although applications are due December 15th, the admissions office will have gone through most of the completed files before then to start making preliminary decisions on who will be invited.
Hope that helps,
Rosanna