Deleting photos

That depends on how and why they were deleted. Do you share an Apple ID with anyone who might have deleted them? If so they should be in the Recently Deleted album, unless whoever deleted them also removed them from that folder. But first, were you saving photos to iCloud? Go to settings, tap on your name, then iCloud. Is Photos turned on? If it is not this is not what happened.

Next check available storage - go to Settings/General/iPhone Storage. How much free space is shown? If it is less than 1 GB iOS might have deleted the photos. If you have ample storage that is not the problem.

So again you can check the Recently Deleted folder to see if they are there.

If if none of this applies you can always restore a backup that contains the photos. This will replace everything on the phone, not just photos.

Your iPhone will never delete your photos unless you have no storage left on your phone. However, if you are sharing an Apple ID with someone anyone you are sharing with can delete your photos.

Then your photos are gone. If you have no available storage you cannot take or save photos. You must copy them off the phone as soon as you take them.