The Cupertino, Calif.-based consumer-electronics company is said to be sourcing new screens that measure at least 4 inches diagonally, according to reports published this week.
Moreover, the forthcoming device received close input from Apple's late co-founder, Steve Jobs, an anonymous source told Bloomberg.
The changes mark the first overhaul of the iPhone since the iPhone 4 was launched in 2010, and the first-ever screen-size change since Apple began manufacturing phones in 2007.
Although Apple's iPhone with its 3.5-inch screen is the category leader, the smartphone market has rapidly expanded to include a number of rival manufacturers offering various screen sizes.
In particular, Apple is facing growing competition from South Korea's Samsung, whose smartphone line uses screens varying from 2.8 to 5.3 inches. The larger devices -- including its flagship Galaxy S2 in the U.S. and Galaxy S3 in Europe -- have 4.3- and 4.8-inch screens, respectively.
A larger-screened iPhone will put Apple not only in line with competitors such as Samsung, but also in line with broader consumer demand.
Indeed, research firm Strategy Analytics released in March a report claiming that almost 90 percent of smartphone owners want a smartphone with a screen in the range from 4.0 to 4.5 inches.
Samsung shipped 26 percent of all smartphones in the first quarter of this year, crowning it the leader with 38 million units. Apple took second place with 33.1 million units.