This is an old revision of the document!
This is using Zextras add-on for Zimbra for mobile device support.
Synchronizing your default Contacts folder is easy and does not require this app to be installed.
If you need to synchronize a shared contacts folder, you can use the CardDAV-Sync Android app. The free version seems to work well on a Samsung S20 phone.
https://play.google.com/store/apps/details?id=org.dmfs.carddav.sync