This site has some of the audio (official publisher's site), and chapter indexes, so we can get an idea of what you should be seeing.
Are you still on chapter one? It looks like it starts out with some basic greetings and phrases (please and thank-you), and perhaps a couple of more specific phrases for classroom use (what is ~~ in Japanese, please repeat that, etc).
I wouldn't worry about memorising the more specific phrases if I were you - I guess that's intended to encourage less English use in class. Move onto chapter 2 which starts on the grammar.
Generally, you do not have to memorise everything in every chapter. Understanding the grammar points is the most important, as this will have a knock-on-effect for later. Learning every single word in the chapter vocab list, not so much.
You can always go back to earlier chapters - in fact, I recommend you do so periodically just for revision.