Ahead of Apple's (AAPL 1.27%) rumored iPhone launch on March 15, investors are hoping the revamped smaller iPhone can help beef up the company's top line, and potentially save the tech giant from a possible year-over-year decline in sales during fiscal 2016. According to one Apple analyst's projections (via AppleInsider), the new mid-cycle iPhone may, indeed, give the company's sales a solid boost.

iPhone 5c. Image source: Apple.

In need of a catalyst
For Apple's current quarter, the company is guiding for revenue to decline about 11% compared to the year-ago quarter. This is a huge change from the company's 18% year-over-year revenue growth during the trailing-12-month period.

The bleak outlook has some investors concerned that the company's sales have peaked; hence, the stock's wildly conservative price-to-earnings ratio of 10 -- a valuation that basically assumes Apple's business will no longer grow.

With this guidance it mind, it's no surprise that Apple is reportedly planning to launch an iPhone about six months before it normally does. Management is likely hoping the new iPhone can reinvigorate iPhone sales growth, and help it resume revenue growth after the current quarter.

If you've missed the rumors, this expected iPhone launch is aimed at replacing the company's iPhone 5s, which Apple CEO Tim Cook said during the company's most-recent earnings call is still selling well, even despite being two-years old. Expected to sport a four-inch display like the iPhone 5, 5c, and 5s, the phone will likely attempt to strengthen Apple's position at a lower price point. Apple is still expected to introduce new flagship iPhones in the fall, as it usually does.

While the phone is rumored to be introduced on March 15th, and to go on sale as early as March 18, investors shouldn't expect the phone to play a key role in boosting iPhone sales for the current quarter, as the current quarter closes at the end of March -- though an impact on the rest of the year is likely.

The path to $5.5 billion
Apple's new, four-inch iPhone could help the company sell an additional 10 million iPhone units in fiscal 2016, adding $5.5 billion incremental sales, according to RBC Capital Markets analyst Amit Daryanani. These expectations -- for incremental iPhone unit sales and revenue -- factor in potential cannibalization of flagship phones, according to the analyst.

iPhone 5s.

With Apple's annual revenue currently at $235 billion, $5.5 billion in sales could add more than 2% to Apple's top line -- potentially enough to help the company avoid a year-over-year decline in fiscal 2016.

Daryanani believes the new iPhone, which is rumored to have a starting price of $450, could boast an average selling price of $550 -- only $140 behind Apple's average selling price for iPhone sales across all of its models. At this average selling price, the analyst estimates the new iPhone could contribute 2% of incremental EPS for Apple in fiscal 2016.

Some of the primary buyers of the new, smaller iPhone, according to Daryanani, will include those who currently use an iPhone three more years older, and India.

Cook did give a nod to India in the company's most-recent earnings call. Discussing the current environment leading to Apple's guidance for a year-over-year decline in revenue, Cook said, "We've also seen these times as opportunities to invest in new markets, just as we're doing now in areas such as India and other emerging markets."

Given that iPhone sales account for more than 60% of Apple's total revenue, a mid-cycle iPhone would almost certainly be accretive to the tech giant's business. And Daryanani's estimate that the phone could add about 2% to the company's bottom line does seem conservative. Even more, these estimates for what a refreshed three-year-old iPhone can contribute to earnings highlights just how important the segment is to the company.