Lost iCloud photos from 2018-2023 and I have backed up my phone to iCloud, and had different phones in this timr

You may be conflating iCloud sync with a backup made and stored on iCloud. Your iCloud backup of your device will include most of your data. But, if you sync photos to iCloud, they will no longer be part of the backup as those are already synced in iCloud. If you sent the device away, and did not log out or turn off iCloud, it's possible that the repair process deleted all of your current data on your device, which in turn updated iCloud and deleted all images. In that case, you might find your images in the Recently Deleted album at iCloud.com/photos.

All that you can do is to restore from your backups that you keep of your most important data.

You’ll need to recover from your backups that you keep of your most important data. If you did not use iCloud Photos, any pictures you had would have been in your device backup that you restored when setting up your new phone. If you use iCloud Photos, your photos available to you remain in iCloud.