Without having all details about your IT environment, I assume that your pictures were stored in iCloud Drive. You have to get them into the photos app to make them synch over to the iPhone.
If you have a Mac, you can open iCloud Drive in Finder, and easily drag & drop pictures over to the photos app.
On the ipHone, you can open the relatively new files app, mark pictures there, and "share" them over to the photos app. Of course you can also open & view pictures right within the files app, but less conveniently than in the photos app.
Maybe there are easier ways that some Apple gurus who know more than I do know of.....