To access iCloud Drive on iPhone, open the Files app, tap Browse, then tap iCloud Drive to view all your folders and documents.
iCloud Drive has to be enabled before your files will sync to the phone .
This is the method you'll use day to day.
One detail confuses a lot of people.
You can also pull a file straight into the app you want to edit it in, which saves a step.
Read the complete breakdown, fixes and what happens next.