I have in the meantime run this:
/usr/bin/php /var/www/fspbx/public/app/xml_cdr/xml_cdr_import.php
that brings some of the calls in, but not all. And any new ones don't appear until I run that again (but again not all do once I do run it). I presume there is some cron that should be running to post the cdrs but I'm not sure... and of course that doesn't explain why not all of them are there once I run it manually.