A solution was provided below but it does not explain why your code doesn't work and that's the important part.
There are two problems.
1) When you're plotting in a loop (which often can be avoided), you need to 'hold' the axes to prevent the plot from being over-written on each iteration. That would look something like this:
figure
ah = axes;
hold(ah, 'on')
for
plot(ah, x, y)
end
2) On each iteration of your for-loop, you're plotting a single point and since you didn't specify a marker type, plot3 is trying to draw a line. You can't draw a line with a single point which is why your plot ended up completely empty. One solution would have been to specify a marker type :
plplot3(p, p.^2, p.^3, 'bo')
But the best solution is to avoid the loop altogether as is demonstrated in the answer below.
