Why does iCloud Photo Library use more space on my iOS device after I configured Upthere to connect to my Camera Roll?
Users of iCloud Photo Library may find that connecting their photo libraries to Upthere temporarily causes more space to be used up on their local device. This is because the Upthere Home app downloads the full resolution photos from the iCloud library prior to uploading them to your Upthere account. If you have "Optimize iPhone Storage" setting enabled, the space used by the downloaded photos will be automatically freed up by the system. There is no way for Upthere app to expedite this process.