I suppose you are on 18.10 as well, so you may want to join in on https://forums.ubports.com/topic/2140/how-to-setup-crossbuilder-in-ubuntu-18-10 instead.
@thepeter just to add that if /data doesn't contain system-data and user-data (better said it is just empty) thing that might help is on phone side mounting it by:
mount /data
that should help (thanks to people in telegram group for quick help)
Offline
