Just move the iPhone up and down while looking at the blue part of the address bar in Safari. Little lines should appear on the screen.
I see what you're looking at. They seem very regular though, which indicates to me that they're scan/raster lines, which would be normal. Most LCD displays have a refresh rate that's part of normal operation, and some people can notice this more easily than others. I wouldn't be surprised if this display has a slower refresh rate than say, a flat panel display or a Laptop LCD, because the power consumption requirements are more stringent.
Unless the pattern you're seeing is irregular, I wouldn't call this a defect, just an artifact of current LCD display technology.