Hi there,
I was in fact interested in Columbia's Japanese Pedagogy program that uses the ACTFL Certified Oral Proficiency Testing program, typically conducted through telephone. Although it seems to me that your Japanese language interview is not a "examination," I'm sure that your interlocutor will use the same criteria that the ACTFL uses to asses levels of Japanese oral proficiency. That is, I would be extremely comfortable talking about my academic interests. Your interviewer would then structure his/her questions based off the level of proficiency you demonstrate. For example, if you are interested in the political/literary ramifications of the
Chusei era, would you be able to address and segue into current political tensions in the United States if your interviewer asked?
Especially that many East Asian Studies programs are straight-track PhD programs, I'm sure that you will be up against some competition. However, if you are able to make in advance some "canned ideas" that you can insert into your dialogue, that can only help you. Also, don't be afraid to have a piece of paper with an outline of your academic interests; that way, you can consult it while you are on the telephone. I have done a telephone language interview several times, and they typically throw in one "curve ball" question (i.e., one that would require some linguistic finesse to answer).
Best of luck to you. Zehi gambate kudasai!