Against a large screen for iPhone

Mr. Cok,
we are glad that we can still keep and use our iPhone with one hand. We see on the 4-inch - display enough to read news daily for several hours each day as well to play games of all genres. Should we even need a larger screen, there is the iPad. Should anyone need an intermediate size, there is the iPad mini. Please do not enlarge the iPhone.
Should it be even larger, many users will switch to smaller competitors products.