The goal of each step is to weed out the maximum number of applicants possible that you actually want weeded out. A quick FizzBuzz before the phone screen should clear enough of a number out to justify its existence.

And, again, it should be something doable in under a minute. The best I've seen is a bonus screen on Indeed that has one of a dozen sample 20-line programs and you just have to point out which line is incorrect in the program.