What year do you think that Apple will stop making iPhones?
I don't think they ever will. Think about it - every year, Apple comes out with an iPhone just a little bit thinner (centimeters), with a better camera, and a higher resolution (think retina display). So, as long as they can improve the thickness, camera, resolution, etc. of the iPhone, they'll keep churning them out. If you have the iPhone 7S (or whatever they'll call that generation), and Apple tells you, "Customer, our iPhone 8T647H9, is 2 cm thinner AND operates 0.0002 seconds faster," you'll buy a new iPhone. This is a trend called planned obsolescence, where a product is planned to go obsolete or become "unfashionable," so instead of buying one iPhone and keeping it for years, like you would a microwave, dishwasher, etc., you buy a new one EVERY YEAR. Think about the iPad Pro. It's a bigger version of the iPad, which is a bigger version of the iPad Mini. Change the size, slap a new name on the product, and you've got yourself a mint. Very smart, Apple.