A long time ago, when I was a fifth grader, my math teacher always said that the day before a test all the students should go to the cinema with the significant other instead of learning, because learning should be finished at least two days before a test, because our brain works on a free day in the background and, without observing, we'll have a deeper knowledge at a test. I've always followed this advice and this was very useful at university. I didn't learn at all before most of my exams because whenever I was at the university, I've payed attention to the teacher, had a lot of time to digest the information and, as a result I didn't have to learn before the exam.
A very interesting fact is that I didn't pass at first try in C++ at the university, because it was the third exam in 3 days and I started to sleep at the time of the exam because of exhaustion (I was lazy in that semester and did all the labor projects in the last day and read a book of 400 pages before the exam). I had fundamental, deep knowledge for a student in C++, but I failed because I didn't pay attention to the most important aspect of the exam: To be there 100% and try to prove that you're the best.
Before the second exam occasion I've refreshed my knowledge in C++ with 2 days before the exam, relaxed the day before and had an excellent result.
It's very sad that you're in such a desperate moment, but look at the bright side: at least you've learnt that you need time to relax before an interview and the case is not lost yet. Let's see the battlefield:
you have worked in C++ before (probably you still have some memories)
you've forgot a lot of things
you have very little time
the interview will be on phone (!)
What can you expect:
simple questions (asking about definitions)
testing your insight
hardcore questions and with so little time, you can only answer these if you know some basic information in C++ and can combine them to find the answer for the question
If I were you, my plan would be the following:
1.) Look at all the definitions and memorize the most important definitions (like the definition of a pointer, reference, method, class, object, inheritance, interface, and so on). Write down all the definitions into a file in your computer
2.) Look at some source codes and understand them. Write them into the same file
3.) Sleep a lot
4.) At the time of the interview open the file and use the gathered information when
needed. Whenever they ask you about something you absolutely don't know, just search for the answer on the internet. They might observe that you're using a computer, but that's not a problem in my opinion, because if you are working on a task, any task, you might encounter a problem you don't know how to solve. If this occurs, you just google for the answer and based on your findings you can solve your problem. Just open a few books and sites to be able to search quickly.
If it's explicitly said that you are not allowed to use computers during the interview, then you shouldn't listen to my suggestion, but if not, then you aren't braking any law by doing this. At least if I'd be the interviewer, I'd value your action of using a computer during the interview, because I'd think that you're couragious and inventive, but people are very different and some people wouldn't be happy about this, they want you to know everything from memory (but that only comes after years of experience, not after a learning session. The information learnt in a learning session will be forgotten in five years, but if you worked for years using something, you'll remember that)
Good luck,
Lajos Arpad.