I had the uncompressed 13.1-extras still installed... its zip is stuck on a semi-dead raid. But thanks for the re-up of the compressed ver.
BTW, I was doing some code-diving. If all is done is move the
game\images\extra folder, then, yeah, it's not gonna work. There's a couple of *.rpy files and a couple of *.rpyc (but as I understand it, those get re-compiled at runtime) that have the code for actually showing the images. For completeness, they are:
game\extra_images.rpy and
game\extra_script.rpy.
In 13.1, it looks like
game\phone.rpy was the only place where those are referenced. I've looked at the 13.2
phone.rpy changes, and it still contains the "extra" code from 13.1, just added to it. If I'm reading this right, there's 6 new patreon-sponsor "extra" scenes. Oof. Hopefully some of those patreon sponsors weren't using their real names, or hopefully they don't care that their names are in plain text in this game's source code... just kinda surprised me to see that in there. :-o
My hunch is this: if you copy over the 4 (rpy/rpc) files and the images, then it theoretically should still have that on the phone. Won't have the new images from the 13.2 release, but won't have lost the 13.1 extras...
BUT I haven't test-ran this yet, but will try soon & report-back (hopefully I can remember to do that).
Edit: Will be a while. I forgot that the reason I'd not played this in a while was that

need to restart from the beginning again.