Sharing the same user home folder between distros is not always recommended, especially with the possibility of permission conflicts. You might have better luck with two version of PCLinuxOS, though, since they share the same "engine" under the hood.
What you can do safely is use the same /home partition, with two separate user home folders. You can also sym-link common folders like Downloads, Pictures, Music, Videos, etc, so that you can access the same files from the same folders, no matter which distro or flavor you boot into.
Here is an example of how this can be done:
# Remove the empty folder first
# Create a new sym-linked folder, that will point to the kdeuser Pictures folder
ln -s /home/kdeuser/Pictures Pictures
Now, whichever flavor you boot into, /home/kdeuser/Pictures and /home/phoenixuser/Pictures will contain the same exact files, every time, and they can both be treated as normal folders. So if you're booted into KDE, you would see all your pictures under your Pictures folder, and if you reboot into Phoenix, your Pictures folder will show the same files.