I had a recent phone interview, also not in my native tongue. My voice does not transmit well over the phone, and especially older people often have trouble hearing me.
My action plan:
First, I went to a nearby family home in the country, where I knew I'd have quiet and access to a land line. Second, I read my interviewer's bio. Third, I decided to stick post-it notes that addressed:
-what had occupied the chief good and market of my time over the past year
-why I wanted to attend that program (here, if you don't already know, emphasize compatibility--remember you are right for the program, your work fits in with what your professor does there)
-plus some good questions that I knew would animate my particular interviewer
To warm up, I spoke with a couple of friends about an hour before to practice speaking in the language, and they gave me pep talks. After the interview, I wrote the person a brief "thank you" email.
You probably know your research better than they will. In my interview, we only spoke casually of my intended course of study, as my interviewer had a different research interest. Couldn't hurt to jot down some potentially relevant phrases about your work in relation to Derrida, etc. My interviewer did most of the talking, which was fine by me--they are also trying to sell you their department.
At NYU I only know a few people in the comp lit department, so I hesitate to give advice... I will say I know a bright applicant who was rather risque, in-your-face who got in all the top places except NYU. Since my writing sample was already pretty racy, I played a very focused application at NYU, and I got in.
You've already made it past the first round. You'll get it. And maybe I'll see you there in September.