Do you have it set to back up/sync pictures with gmail, google drive etc.
They may be in your account.
You could try to download a different gallery app, to see if it loads anymore pictures.
Were the pictures on the phones memory or an SD card?
If the SD card is corrupt, pictures might not show on your phone,
but can be found with a Photo Recovery app on the Play Store.
I also have used Zar on my PC with good results.
https://www.z-a-recovery.com/tutorials/digital-image-recovery.aspx
