It iw not that difficult. You will need knowledge of basic JS like use of Arrays, if/else , some array methods like forEach etc. There will be some pseudo coding challenege but they are very easy and even if you have never done pseudo coding before the instructions are super easy to follow.
And about the phone interview, just share your experience, goals, what are you looking to get out of the course. Be honest and if you are motivated and really want to learn the interview will be a piece if cake. Good luck.