Despite the latest rounds of super-gigantic iPhone screen size rumors, iMore is hearing that, as of last month, plans for the new iPhone (iPhone 5,1) called for the same 3.5-inch screen as previous generations. While we're told that isn't set in stone, and it's possible Apple could go slightly bigger, there's doesn't seem to be any chance for anything even approaching the size of a Galaxy Nexus.
Not only does that come from a good source, but it stands to reason. First, Apple has put a tremendous amount of time, energy, and marketing into the concept of a Retina display. With a Retina display, density can get lower as distance increases -- that's why the new iPad's 2048x1536 Retina display at 264 ppi doesn't need to be as dense as the iPhone 4S' 960x640 Retina display at 326 ppi. -- but Apple probably wouldn't push a 960x480 display to 4.65-inches and settle for 248.12 ppi.
They probably wouldn't bump up the resolution either, because it would break compatibility with existing software. That's something they deliberately avoided in the past by exactly pixel doubling the older screen resolutions to get to the Retina display, rather than going with an arbitrary size or standard resolution like 720p.
Apple has also paid attention to one-handed ease of use, keeping every inch of the iPhone screen easily accessible -- if held in one hand, most people's thumb can still reach the opposite corner without much difficulty.
Surveys have suggested users would appreciate a larger screen on the iPhone, and perhaps Apple would consider something up to 4-inches. At 960x640, a 4-inch screen would be 288 ppi. A 3.75-inch screen would be 307 ppi. Both are lower than the iPhone 4S but still higher than the new iPad, but they'd let Apple maintain the current resolution and much of the one-handed ease of use.
Nothing bigger than that seems likely, however. Apple also has a way of disregarding market research. The late Steve Jobs liked to quote Henry Ford: "If I had asked my customers what they wanted they would have said a faster horse."