OneDrive attachments

Hi WadeSwiger,

Thanks for following up.

Check out the steps in the following article: Use the Files app on your iPhone, iPad, or iPod touch - Apple Support

"Use third-party apps in Files

The Files app lets you add your third-party cloud services — like Box, Dropbox, OneDrive, Adobe Creative Cloud, Google Drive, and more — so that you can access all of your files on all of your devices. The files you keep in iCloud Drive automatically appear in the Files app, but you need to set up your other cloud services to access them in the Files app too.

Add third-party apps

1. Download and set up the third-party cloud app.
2. Open the Files app.
3. Tap the Browse tab.
4. Tap More  > Edit.
5. Turn on the third-party apps that you want to use in the Files app. 
6. Tap Done.

If you don't see one of your third-party cloud services in the Files app, check with your cloud provider.

On iOS 12 or earlier, open the Files app then tap Locations > Edit to add third-party apps.

Move third-party cloud files

1. Open the file that you want to move.
2. Tap Share  > Copy.
3. Open the folder where you want to move your file.
4. Firmly press the screen.
5. Tap Paste."

Kind regards.

Greetings WadeSwiger,

Thanks for visiting the Apple Support Communities! It seems you'd like to select a OneDrive file as an attachment when sending mail on your iPhone.

Are you able to add a file from OneDrive by selecting Files > Browse, then select OneDrive under Locations when adding an attachment?

You're welcome to leave feedback to Apple directly regarding attaching files to mail on iPhone: Product Feedback - Apple

Cheers.