Apple’s latest iPhones support Apple’s RAW format, ProRAW. You can enable ProRAW on these devices and capture ProRAW images using Apple’s Camera app. Apple provides step-by-step instructions on how to enable ProRAW:
https://support.apple.com/guide/iphone/take-apple-proraw-photos-iphae1e882a3/ios
If you have an older iPhone or want to use a third-party app to capture RAW photos, we found a handy how-guide for RAW iPhone photography on iMore.com:
https://www.imore.com/how-shoot-raw-photos-your-iphone-or-ipad
iMore also has a guide for third-party RAW camera and editing apps: