Restoring photos to iPhone photo albums

Is the only way to preserve the iPhone photo albums to copy them over to the iXpand album by album?

I copied all 2017 photos over onto the iXpand and deleted them off the iPhone (although they are all still in the “Recently Deleted” album on the iPhone).

But I wanted to keep them organized by the same albums.  

I guess I thought the photos would still display in the iPhone photos app in their native albums but would be stored on the iXpand rather than in the iPhone.  I didn’t realize that the iXpand would really act more like a PC flash drive.

Help please!

Correct. If you want to preserve the album sorting you would have to create a folder for each album and copy the photos from each album into the corresponding folder. 

Once the files are transferred to the iXpand the native photos app would not see the photos. you can delete the files from the iOS device but to free the space immediately you would need to go delete all the recd photos. Otherwise iOS will keep them for 30 days IIRC before they are fully deleted. Once that is done you would have to use the iXpand drive app to view photos stored on the iXpand. 

Have you tried Icloud for restoring it?