Calls ring to your cell phone just like a regular phone call, just with a different ringtone and vibration pattern. To answer a call while your phone is locked, simply slide the Slide to answer slider to the right

 

If you wish to ignore the call, simply double-press the lock button

 

If you answer the call while your phone is locked, you will not be able to do call control actions (e.g. place call on hold, transfer, etc.) since the phone is locked. You can unlock your phone and get to the call control by tapping the Webex icon on the screen after the call is answered:

 

While your phone is unlocked, incoming calls will display at the top of your screen. You may answer the call by tapping the blue checkmark icon or you may ignore the call by tapping the red x icon

 

You can also tap on the name of the caller to expand the call notification window