Native portrait Zoom Rooms mode is not currently possible with the Yealink A30.
Your best option (which, to be clear, is a bad option) would be to scale a landscape 16:9 into the portrait view and lose a chunk of your screen real estate. This would require a capable display or hardware scaler with rotational capability.
If the displays are right next to each other and have small bezels, you could theoretically run them out of a video wall processor (2x 16:9 screens in portrait would equate to 9:8) and get them to form one massive screen that's a bit closer to 16:9. Still not ideal - most bezels would rule this option out.
The only appliance capable of running Zoom Rooms in portrait mode (to the best of my knowledge) is the Neat Frame, which is not even included on the Zoom Rooms Certified Hardware list (this is classified as a 'personal' device). Definitely not the norm or an expected use case.
I don't want to yuck your yum, but I personally would never wish to view a 55" monitor in portrait mode for conferencing, especially with how Zoom preserves 16:9 resolutions (unlike Teams).
Hope this info helps!
