I have been looking for the same capability;
I am too stingy to pay for a PlexPass to enable their automatic backup; but I have recently found that DropBox (sort of) has that functionality. (This app will upload to the Cloud. Presumably, from the cloud I can easily download to a MPWP or somewhere else in my network).
One problem with the dropbox transfer is if you use the “live” function of iOS picture taking. The dropbox transfer appears to ignore the “live” aspects and only transfer the still JPEG. (If you plug the iOS device into a USB connection, you will find that there are both JPEG and MOV versions of each photo -> I suspect dropbox only copies the JPEG).
I suspect the plex functionality will work the same way.