The holiday quarter is always Apple's (and most retail companies') biggest money making period of the year. 2015 was no exception. Apple sold 74.77 million iPhones over the past three months.
What's unusual about that high this year, though, is it's essentially the same as the sales peak Apple hit last year after the iPhone 6 and 6s were announced: 74.5 million iPhones. Up until now, each year, iPhone sales have grown significantly. With this quarter, it's finally leveled off.
With that in mind, Apple's areas of growth continue to be emerging markets (China and India, in particular). As LTE coverage expands globally, people who don't yet have reason to buy an iPhone may be able to purchase one.
Apple's iPhone sales leveling off isn't a sign of impending doom for the smartphone market, the iPhone, or Apple itself. The Cupertino company still makes a boatload of money (it's quarterly revenue record this time around: $75.9 billion), and now sees one billion active Apple devices across the globe. While we may have hit peak iPhone in sales, rest assured, you're not going to stop seeing them any time soon.