Apple was originally meant to be sourcing its 128-bit 3D NAND flash memory from Yangtze Memory Technologies (YMTC) -- a Chinese supplier -- but because of the US trade ban with China, the company can't do that and now needs to work with Samsung to get memory chips into the iPhone.
The iPhones sold in China would've used the Chinese-supplied memory chips, with Apple reportedly prepared to source around 40% of all of its iPhone memory chips from YMTC, but not anymore according to sources at DigiTimes. The site reports that Apple is now working with Samsung -- which is one of the largest memory manufacturers in the world -- to make around 40% of its iPhone memory chip orders.

Samsung is already working with Apple to supply displays for the current-gen iPhone 14 Pro and iPhone 14 Pro Max smartphones, and with new contracts for memory chips, Apple's main competitor is putting more and more of its technology into its competitors' smartphones.
Western Digital and KIOXIA, as well as two Japanese companies, are making memory chips for Apple's new iPhones, while South Korean memory giant SK Hynix is making the remainder for Apple. We don't know how many memory chips Samsung will be making for Apple, but considering YMTC was making 40%... it wouldn't be a small order at all, that's for sure.