There are two kinds of patents: design patents, which protect the arbitrary look of a product, and utility patents, which protect a technology. The relevant patents here are design patents that address the recognizable "look" of the iPhone (rounded corners, colored border, etc.).

These are arbitrary choices, and that's precisely why it isn't rent-seeking to protect them. There is an infinite number of arbitrary designs that would achieve the same function; the only reason to use the ones Apple chose is to try and trade on the consumer goodwill Apple has created with its products, or confuse people into associating your product with Apple's. Those aren't legitimate bases for competition; they are free-riding (a concept at least as important as "rent seeking").