It's all about the replacement cycle.
From Barron's A Ray of Light for Apple ($):
Alas, with 3 billion smartphone subscribers worldwide, and paltry 1.2% growth, it appears that the smartphone market has fully matured. That’s hurting shares of the devices’ makers. Samsung Electronics stock dropped 17% in the fourth quarter, Apple (AAPL) lost 30%, and Apple suppliers that Barron’s tracks fell over 20%, on average. Investors could be worried that they have to wait for 5G before smartphone growth accelerates again, but mature markets have an additional growth card to play—replacement cycles. And the phone replacement cycle should help out the sector in 2019.
Replacement cycles are often an important source of demand for mature industries. For instance, industrial companies Dover (DOV) and Fortive (FTV) have been growing their fueling businesses by double-digit percentage points because of a replacement cycle for gas pumps.
Gas pumps outlast smartphones. According to industry surveys, people are holding on to smartphones longer, but still replace them every two to three years.
We estimate that old phones—which are prime for replacement—represent over 12% of the smartphone installed base today.
My take: Someday those fossil fuel pumps may be mothballed for good. Electric Apple car, anyone?