Usually if they don't download from cloud backup if they are not on the phone.
Could be it's not a format that is compatible. Like RAW photos from a camera or photos from some other means.
Could be corrupted files.
Are these photos taken with that phone?
Is it a new phone you are setting up?
Are these cloud storage files you are trying to access or on the phone?
Do you have the photos backed up in a different cloud storage?
