file sharing with another iphone user

If the phones share an Apple ID anything saved to iCloud will be accessible to both phones. However, this is not a good way to do it if the phones are used by different people; in that case the phones should have separate Apple IDs. If the files are photos you can create a shared photo album that can be viewed by anyone you authorize. For other files that are in iCloud open the Files app on your phone, hold a finger on a file, when the menu pops up choose Share, scroll down and choose “Add People” and choose a way to send the invitation.

Then you are probably better off with Dropbox, box.com, Microsoft OneDrive, or Google Drive. All of them have apps for iOS as well as Mac, Windows, Android, Linux etc. and all let you share folders.