Missing pictures from icloud

Were those older photos ever sync'd from a Mac or a PC? They would not be in iCloud Photos.

If they are not in the phone, not in a computer and not in iCloud Photos then there seems no possibility of recovering them.

Any browser like Safari,

Type in icloud.com in the address bar.

It may send a two factor authentication code to another device or to your phone if you are using Safari on there. Write down the code, tap OK, then type the code in the 6 boxes.

Tap on the photos icon.