Apple (NASDAQ:AAPL) is conservatively valued, with a price-to-earnings ratio of just 13. Even more, it could be argued that the market has priced the company for zero net income growth going forward. But does a valuation this conservative make sense in light of continued opportunity for Apple's largest and most profitable business segment?

Apple's iPhone business accounted for 56% of its fiscal 2014 first-quarter revenue, and an even larger portion of is operating profits. As such a large portion of Apple's business, the segment will probably be the biggest driver for Apple stock in the coming years -- even with new product categories on the horizon. Fortunately, several factors point to more growth for the business.

As Fool contributor Daniel Sparks points out in the following video, a growing iPhone business could make the stock undervalued at today's prices.