How can I retrieve lost iCloud pictures?

If you delete from iPhone they are gone from iCloud too.

You post does not specify exactly the process adopted by you.

If it is not in the Recently Deleted Album then either you have deleted them 30 days earlier or have never deleted any.

Please check the following

1. If you have restored your iPhone with a backup which does not contain the Photos that you are looking for then please look for correct backup on your PC/Mac --> Locate backups of your iPhone, iPad, and iPod touch - Apple ...
2. Probably you may have un-synced photos with Mac / PC, sync them again
   1. For PC: --> Sync photos in iTunes on PC with devices - Apple Support
   2. For Mac --> Sync photos between your Mac and iPhone or iPad - Apple ...
3. Have you ever imported your photos to Mac/PC and used Delete after Import --? Transfer photos and videos from your iPhone, iPad, or iPod ...
4. Do you have a backup (iTunes) --> Restore your iPhone, iPad, or iPod touch from a backup ...
5. Have you ever uploaded them to any Cloud Drives Cloud Drives (iCloud Drive, Google Drive, OneDrive, DropBox, Flickr, box, AmazonDrive, Adobe Creative Cloud etc)