If what you want is to move the pop up windows to the bottom instead of the top, I don't think you can do that. But you can always try going to the Phone dialer settings and turn off the option of Shows calls in pop-up and then do a test call to yourself to see if you like what it does then.
Also, you don't need to answer calls by pressing Answer, if you go to Settings-Accessibility you will see an option for Answering and Ending Calls where you can turn on the use of the Volume up to Answer a call and power button to end it.