Earlier I said:
This page has a pretty good tutorial and specifically targets DAVdroid:
In the problems section are these 4 items:
Check that the Calendar Storage app on Android is not disabled or missing.
There is no such app on the phone or on f-droid.org. If this is a
requirement, it seems like a show-stopper and an anti-feature.
Turns out that Calendar Storage and Contacts Storage both exist and
are running. Also, thanks to a hint from the Replicant list I investigated
possible permissions issues. I finally found that there was a check-box
for "Enable Privacy Guard" that I had to un-check. After that the sync
worked. It took a long time but I now have the address book and calendar
on the phone.
PS: I have no-script enabled in my browser and I allow the minimum amount
of non-relevant sites for privacy. I am not on twitter, therefore digging
for twitter information shouldn't be relevant, yet it was not possible to
post this reply until I allowed twitter.com so this web site could go
snooping for twitter information. Not user-friendly. Twitter information,
especially if it's not relevant, like in my case as there is none, should
not be a pre-requisite for posting a reply. Yet another reason why I prefer
email lists to forums.