Unfortunately, the phone cannot handle CardDav directly. However, there are services on the net that convert this into the Yealink XML format, there are also scripts on the net and of course the AI that supports this very well.
The solution to this is probably RemoteTelephonebook.
Here is some more information.
http://www.lambrettaclubtoscana.it/wp-content...
That's exactly what the adapter is for. If possible, a wired solution is certainly always better, but if this is not possible, you can rely on the adapter provided you have good WLAN coverage.