Excerpt from linked documentation (emphasis mine):
When you enter your username and password, you will receive an automatic push or phone callback. Alternatively you can add a comma (",") to the end of your password, followed by a Duo passcode.
So, use the token passcode as your Duo passcode.
It’s also a good idea to have more than one device enrolled in Duo as a backup, like a landline or Google Voice number. Then you’d specify the other phone with password,phone2.