Touchscreen smartphone dial-pad design has not been changed since 1963 (when it was designed for push button phones). As the size of the phones increase it is becoming harder to reach certain regions of the screen while holding the phone to dial phone numbers.
This UX research study is to evaluate performance of alternative dial-pad layouts for smartphones.
You can read more about the research here: http://ssdesigninteractive.com/dialpad_research/
and here is the medium article
https://goo.gl/tVK1eu