Actually iPhone sales have been falling.
They sold 37.4m iPhones in 2013Q2 and 43.7m iPhones in 2014Q2. That's a year-over-year increase of about 16%.
I'm afraid you fell for a classic misleading graph.
I didn't fall for anything, that article is just dumb. It makes no sense to compare quarterly reports with immediately preceding quarterly reports for highly seasonal products like the iPhone because different quarters perform differently.
Of course if you look at the numbers that way in early September 2013 you're going to see decline - that year's iPhone model was released in late September. iPhone sales spike after launch and during the holidays, tail off through the rest of the year, then spike again when the next model is released. You can only gauge trends properly if you compare year-over-year numbers. And the year-over-year numbers show that iPhone sales are continuing to grow.