To avoid the awkward situation of answering an Xbox One Skype call while completely naked, Microsoft released a full list of Kinect voice commands and gestures.
Answer Skype calls without video recording with the command "Xbox, answer without video." If you want to embrace the awkwardness, make a fist to grab the screen and zoom in on the incoming picture.
Other more practical voice commands should help Xbox One users take full control of the Kinect's capabilities. If you accidentally trigger the Kinect's voice controls or no longer need it to listen for commands, "Xbox, stop listening" dismisses any voice commands the Kinect expects.
For the full list of commands to quickly record videos, invite friends or end that awkward Skype call, you can download a PDF of all functions here.