I think I may have discovered something unique to mathematics. I made a (sloppy) webpage to explain:
What pure nonsense, surely this is a joke right?. The relative size of those cascading images you got when you pointed your webcam at your monitor are simply a function of the relative size of the camera's field of view and the size of the screen.
Also you don't even know the difference between +ive and -ive feedback. When you point the camera at the screen it's actually positive feedback, not negative as you claim. Positive feedback doesn't necessarily lead to a system that blows up exponentially, if the loop gain is less than one then positive feedback systems are also stable. Also negative feedback system don't necessarily oscillate, there is so much rubbish on that page it's ridiculous.
regardless of whether its positive or negative you still get phi. I've done it more than once using different angles with different measurements. The size of my monitor or the field of view of my camera have nothing to do with it. Try it yourself and you will get phi also.