For anyone interested, 'Phase Space' can be easily described by a simple moving pendulum. You could plot its height above the ground on the y-axis, and its position either side of the centre along the x-axis (you'd end up drawing an arc of a circle).
To get the phase-space, you could also plot its horizontal position (over time) on the x-axis, and its velocity along the y-axis. This ends up as a (sort of) ellipse.
Here's a good animation showing some phase diagrams of a pendulum in motion.
Cheers