Apple designs the chipsets used to power the iPhone, and then turns over the manufacturing to a company with the facilities to produce the component. In the last few years, Samsung and TSMC have been given the task (exclusively, or together) to produce these chips. TSMC has beaten out Samsung in the race to the 7nm process and according to industry sources, Apple has given the foundry an exclusive to produce the A12 SoC that will be used on the 2018 iPhone lineup. TSMC already has orders from 40 customers to produce chips for mobile devices, using the 7nm process.
The A11 bionic chipset is produced by TSMC
TSMC reportedly plans on keeping the pressure on Samsung. It will incorporate extreme ultraviolet (EUV) technology into its 7nm+ process, and will continue working toward developing the 5nm and 3nm processes. The company is building a new plant that will be used to test the 5nm process in the first half of 2019. In 2020, a fab that will produce 3nm chips will start construction.
The 2017 Apple iPhone models use the A11 bionic chipset that is made by TSMC using the 10nm process. It is Apple's first SoC to carry a hexacore CPU, and features two cores for heavy duty tasks that are 25% faster than the A10 chipset. The remaining four cores are power efficient and are 70% faster than the energy sipping cores used on the A10.