When you receive a call, you can either answer the call or silence the incoming call alert.
Silence the incoming call alert
Tap one of the Volume keys when you get a call.
The incoming call alert is silenced but the call continues until it's ended or diverted.
Answer a call
If the screen lock is turned on, tap and drag the accept call icon right.
If the screen lock is turned off, tap Accept.
Tap the end call icon to end the call and return to the home screen.