@keneda
Thank you for your reply.
I tried it also with the download folder from ubuntu touch. It has the same affect. The download folder becomes a new owner and group: 1023:1023 and the host (ubuntu touch) has no write access any more. I can only read the files. But apps in waydroid have read and write access.
I tried it also like explained here:
https://forums.ubports.com/topic/7296/is-a-copy-paste-possible

mkdir -p /home/phablet/WaydroidHome
chown phablet:phablet /home/phablet/WaydroidHome
chmod -R 755 /home/phablet/WaydroidHome
sudo chmod -R 777 ~/.local/share/waydroid/data/media/0
sudo mount --bind ~/.local/share/waydroid/data/media/0 /home/phablet/WaydroidHome

It works, but it works only one time. After reboot i must make all steps again.
Ok, i could make a upstart script for that. For now i installed a samba server on ubuntu touch and have now access to the shared folders in waydroid.

Here is the way to go:
https://askubuntu.com/questions/610513/how-do-i-share-a-directory-between-an-lxc-container-and-the-host

Container specific configuration:
lxc.idmap = u 0 165536 1000
lxc.idmap = g 0 165536 1000
lxc.idmap = u 1000 1000 1
lxc.idmap = g 1000 1000 1
lxc.idmap = u 1001 166536 64535
lxc.idmap = g 1001 166536 64535

But that does work on a standard ubuntu installation, not on ubuntu touch, because there are different uids and gids.