Re: How do I access file from iCloud drive on my iPhone 6 plus?
I agree its not as easy and simple as it should be. In fact I rarely use iCloud Drive, partly for those reasons and the fact that I had to get an app just to access it.
To access iCloud Drive from iOS on my iPhone 6+, I got Documents by Readdle. The app supports accessing Dropbox, Google Drive, iCloud Drive, etc. As the iMore article below mentions, you can also access iCloud documents via the apps that created the document originally.
But I don't think there is a centrally available way to access the app like there would be in Windows where you can just go to My Documents (or wherever you keep stuff on your computer), and then open the app in whichever folder you saved the document.
Perhaps others will weigh in with additional options, ideas, or better ways for how to access iCloud Drive from iOS devices.
Clearing up the iCloud Drive confusion: No, there's no iCloud Drive app on iOS! | iMore