Tesla MODEL S Operating Manual page 146

Phone
In Call Options
When a call is in progress, you can display the
call menu on the instrument panel by pressing
the top button on the right side of the
steering wheel. Then roll the right scroll button
and choose an option (see Using Right
Steering Wheel Buttons on page 45). To adjust
the call volume, roll the steering wheel's left
scroll button during a call.
Using the Touchscreen 145