In-Call options
Do not cover the microphone during a call.
During a call, your device will display an in-call menu.
Hide the in-call menu: Touch
Home or Back 
.Touch the green status bar at the top of the screen to return to the in-call menu.
Start a three-way call: Contact your carrier to find out how to use this feature.
Adjust the volume: Press the volume up button to increase the volume, or the volume down button to decrease the volume.
Questions about your Huawei Mate 10? Post in the comments!
Huawei Mate 10 Manual [PDF]