Windows Phone 8 Basics - Share things on my phone - To resolve a conflict

A conflict can occur if you're editing a document from your phone, and then you try to save your changes after someone else has also made changes to the same document on the site. When this happens, you'll need to resolve the conflict before you can save the document back to the SharePoint site.

If the Can't upload message box is still displayed, tap OK.

In the Office Hub, tap and hold the document that has the upload error underneath it, and then tap View status.

Tap Resolve on the Upload status screen.

On the Conflict resolution screen, do one of the following: To update the document on your phone with the latest copy from the SharePoint site, tap Replace item on phone, and then tap Refresh copy. Warning—the changes you made to the document on your phone will be lost.
To save the copy of the document that's on your phone to the SharePoint site, tap Replace item on server, and then tap Refresh copy. Your copy will be saved to the SharePoint site and will overwrite the current version that's on it.
To keep both versions of the document, rename your copy of the document on your phone. Tap Save as, type a file name in the File name box, tap the Save to box, tap the place you want to save it to, and then tap Save. Your version will be saved where you specified, and the other edited version will be on the server.