Pictures are included in the iCloud Backup only if you don't use iCloud Photos. iCloud doesn't keep extra doubled copies.
Were these pictures taken on your phone, or were they transferred to the phone? Some pictures that were transferred from a computer can be viewed in Photos but they can't be modified by Photos, so there may be some operations that produce a warning about those being at risk. So if you’re missing pictures that were transferred from a computer, then you should look on the computer for the originals.
Pretty much, if you don't keep your own backups to an external drive, then there really isn't any place else to look. You can try contacting Apple Support
Connect with live support
but they will first ask about backups. The are generally helpful, but there may be nothing that they can do.
To back up your pictures you can just plug in an external drive, select the pictures, and use Share>Save to Files. Alternatively, you can backup to a computer:
Transfer photos and videos from your iPhone or iPad to your Mac or PC
If you haven't done one of those backups, then your remaining pictures continue to be in peril.