I have Bluetooth off and still I can't answer call. I push the green answer button and nothing. It just goes to voicemail. This is driving me crazy. Other than that, this phone is cool.
I struggled with this too, as it's my first Android. I discovered by accident to SWIPE instead of tap.
Yes, put your finger on the green and swipe to the right.
Seems like Android has a thing with swiping.