It is convenient to use OneDrive for Business to share files. Some files will be shared with external collaborators as a one off, whilst early drafts of other files will be shared with a small number of colleagues in order to solicit feedback. However, OneDrive for Business should not be seen as the final repository for files which need to be shared. For one thing, when you leave the University all your OneDrive for Business files will be deleted including the ones which have been shared (see Finishing IT use at Oxford for further information).
The help page Storing your files explains a variety of places where final copies of documents could be placed in order to share them. Two of the most obvious are SharePoint Online and Teams. In both cases, when you leave the University, the files will remain available to your colleagues (as long as the Teams site has at least one other owner besides yourself).
You can see which files you have shared from your OneDrive for Business account by clicking on Shared in the left hand menu bar. Make sure you click on the By you tab at the top.
If you want to stop sharing a file, hover to the right of the name and click on the ellipsis which appears and select Manage Access.
There is a quick way to move OneDrive files to SharePoint, but only from the MyFiles section and not from the Shared section. To switch section, click on the ellipsis and select Open Location and OneDrive will switch to MyFiles and open in the relevant folder. Select the file, or group of files, in MyFiles and click on the ellipsis , you can select Move to and move to either a SharePoint Online document library or a Teams site.
At this point, you may wish to delete your copy from OneDrive for Business and free up disk space.