I find that buying cheap android phones on Amazon, and installing workplace is a better wifi option than buying the wifi phones, and associated docking stations.
Cheap, familiar to users,Familiar to Admin, and multi-purpose.
That being said, yes, there are Wifi phones available from Avaya.
The J179 ( and some others ) Deskphone has a WiFI option.Need to purchase the optional J100 Wifi/Bluetooth card.
The Avaya Vantage device has WiFi as an option.
There are a few DECT cordless phones that work as well, but you need to deploy DECT access points.