Nyquist with only poles at the origin
Your answer is correct. Each pole gives 90 degrees phase lag. Furthermore, here can you download a file lnyquist1 which is able to give a more accurate result when you have a pole at zero.

num = 1;
den = [1 0 0 0];
lnyquist1(num,den);


In addition, WolframAlpha is also able to give an accurate result, see here.