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When you delete something from your phone, only the reference to that file is being deleted and the actual file will be still there for a limited time and could be recovered using third party data recovery applications. These deleted files will be there until they are over written with new ones. It is possible to retrieve deleted files like photos. But that completely depends up on how much you used your phone after you deleted them.
If you have taken photos or videos, downloaded apps etc after you deleted them then the chance of them getting recovered is slim to none. Because they might be over written with new ones.
The more you use the phone, the more it become hard to recover. However, you can attempt to recover them using the following applications
Dr.Fone for iOS from Wondershare --> https://drfone.wondershare.com/iphone-data-recovery.html
EaseUs --> https://www.easeus.com/mobile-tool/free-iphone-data-recovery.html
Also, go to www.icloud.com, login to your iCloud Photos, click Photos and see if you can find the photos there.
The application are paid ones, so try the trial versions before buying it. Again, I can't guarantee they can be recovered. If you are unable to recover them, please don't rate me bad or poor or ok as this is something I can only give instructions on and the success completely depends up on the factors I mentioned.
If you have any questions or would like any additional information, please don't hesitate to ask.
Note : This is not my final answer. I strive to provide Excellent service or 5 star service. If you feel you've received anything less or if you are not satisfied or if my solutions didn't work, please don't rate me bad or poor or ok as it will badly affect my job here. Instead, please let me know and I will try my best to help you until you are fully satisfied or the issue is resolved.