If they were uploaded to google the following instructions will help you get them from there. If they were saved elsewhere (another cloud account) then you will have to check how their location requires you access and download them. However, if you didn't back them up, and they were just on the device (if it is either damaged/broken or gone) then you can't get the files.
1. Open the "Google Photos" app.
2. Tap the photo you want to save to your phone.
3. Now tap the "Options" menu.
4. And finally tap "Restore".
5. Repeat for each image.
Or, to get them all at once...
1. Log into the google account associated with the app.
2. Download all the images to an empty folder on your computer.
3. Connect the phone to the computer via USB cord.
4. Copy the images over to the phone or sd card.