Do you have access to a computer with an sd card reader? I believe the best and safest thing to do is to connect it to a computer, create disk image from it and try ro use a data recovery tool in the image file.

Edit: if you only have the phone, maybe you could try looking for apps to copy a disk image from the sd card and to recover data or try using some terminal emulator or one of those apps that install a linux distro inside android to use the dd command and then use testdisk and photorec tools. I recommend the second option, because the tools are open sourc and well tested