This is using Zextras Zimbra add-on 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

Add Account → CardDAV → Enter Zimbra URL and Credentials

Leave Use SSL selected.

You can also edit Settings (gear icon) for options like:

• Sync Interval
• One-Way Sync

In the Zimbra Web Client:

ZWC → Contacts (tab) → <your shared contacts folder> (drop list) → Share Contacts Folder

Right-Click the URL → Copy Link Location