If the photos are important to you I would suggest backing them up to your computer / cloud etc. Sdcard should not be the only storage.
Once they are backed up (preferably in more than one location) verify the backups first.
Then you can check the phone /albums and decide what to do.
Usually if you transfer photos to an external sd memory card it "moves them" from the phone to the card.
You should be able to see a little sdcard icon on the album /pictures on your phone... This tells you where the photos are stored.