Mine also does that... mutes the audio automatically, shows the call on screen, then leaves the "phone display" up at the end of the call (although it does continue to play music at the end).
The shortcut is handy - slide the I-Drive knob in the direction that you want to eventually be on the display and hold it for a couple of seconds. For example, you can get from "phone" display to "audio" display by holding the knob towards the back seat for a couple of seconds.
My CA described it as Climate is towards the driver for comfort, Audio is towards the back for the rear seat passengers, Nav is to the right because the "navigator" is traditionally the passenger, and the Phone is ahead because... I can't remember (because the rest were taken???). Anyways... good shortcut!
Let me know if your appointment changes this i-drive behavior.
14 Tesla Model S P85D Black/Grey (691 hp
13 X5 xDrive 35i M-Sport Black/Oyster (Hers)
PAST: 03.5 M3 Cab, 08 E92 M3, 08 535xiT, 07 X5 4.8i, 06 E90 325i, 87 E30 325i, 85 E30 318i