My interview was for the Global Activities Scholars Program, not necessarily my application in general, but I'm sure there would be similar questions. Things like: Why did you pick your practice area and concentration? What do you want to do after you graduate/how can the degree help you get there? I'd also think of 3 strengths and weaknesses of yours and how they might apply to grad school/MSW. Also specific examples of leadership; overcoming a failure; possibly hardship. If you're life story is unusual then be sure to know your narrative and how it translates to an MSW degree and what you want to do with it and you should be just fine.
My interview lasted 30 minutes and I did it over Skype, so don't worry about doing it over the phone. Also, don't be afraid to take a minute or two to think of your response. Silence is awkward on the phone, so a lot of us feel the need to respond right away. There's nothing wrong with saying, "let me think about this for a second," while you compose your answer.
Good Luck!!