In Voice Assistant under Settings, I have 2 “Assist Devices” that have been auto-detected. Opening that option reveals two IP addresses on my lan that correspond to my two IP desk phones. I’ve not tried to configure these with Assist - it found them by itself.
That said, I can find no way to actually use them with Assist, and no documentation that suggests any way how. Surely, if an analog phone with an ATA can be used, then a native IP phone should be a snap - but how?
Curiously, I also have an IP Phone built into a Door Intercom which was not found by Assist - but it could be fun to have a virtual Butler answering the doorbell 
Am I missing something obvious somewhere?