Photo stream only keeps photos in iCloud for 30 days, and can only be accessed by your computer if it is signed into your account with photo stream enabled.. Older photo stream photos are no longer in iCloud. If the photos were in the camera roll on your phone when you last backed it up, restoring the entire backup to another iPhone should recover them. If you have a backup of your phone on your computer, you could also try to extract the photos from the backup using 3rd party software such as iPhone Backup Extractor.