Most Android smartphones integrate some type of technology allowing users to interact with their devices through motion gestures. On the Sony Xperia series this feature is called Smart Call Handling.
This tutorial explains how to enable and use Smart Call Handling. You can, for example, answer calls by bringing your device to your ear, mute calls by flipping the device face down and reject calls by shaking the device:
Go to Apps > Settings. Scroll to the Device section and then tap on Personalization:
Tap on Motion - Control your Xperia using motion:
Tap on Smart Call Handling:
Toggle the Smart call handling switch On and that's it: