Okay, when I edit the config in home, it does work, so it's the
config-file switch that doesn't work.
$ phasex --help
-c, --config-file= Alternate config (takes precedence over default
config file and command line options.
I hope MIDI maps can be stored or edited by an editor and then restored
too. Fortunately the naming for the options is easy to guess, so I was
able to edit it to my needs.
FWIW there's an entry that might be related:
# warning: backing store may be broken
backing_store = off;