They are part of the same app but totally different apps and design 

Here is the Phone(dialer) part of the app: https://github.com/mozilla-b2g/gaia/blob/master/apps/communications/dialer/index.html
and here is the on call(calling menu) part:https://github.com/mozilla-b2g/gaia/blob/master/apps/communications/dialer/oncall.html