Can aluminum foil damage my iPhone?

I'm trying to block the GPS signal of "Find my iPhone" from my parents. If I wrap my iPhone 4S in aluminum foil, will it damage the screen or anything else?

It might well cause some cosmetic damage.

If you leave your phone "on", it will flatten your battery in very short order.

Turning your phone "off" will defeat most apps. If you are extra paranoid, wrap it in a layer of cotton cloth (a bandana would be perfect) before the layer of aluminum foil.

It won't damage anything, but unless you wrap it completely, it won't block GPS or other signals, either. And if you do wrap it completely, you won't be able to use it. You can't block signals to and from the phone and still use it for anything that requires those signals, and since it must be completely enclosed with metal to block the signals entirely, you can't use it at all when it is entirely wrapped (the touch screen in particular will not work, although you wouldn't be able to see it, anyway).

You can turn off Find My Phone if you know the password of the Apple ID with which the phone is associated.