Ah, yea Xposed would do the trick, if rooted. If you aren't rooted, then using another app like I posted would be about the only thing. You still place calls like normal, just when you go to answer, it'll pop up with the app / full screen that can be themed and all that. It doesn't have it's own dialer UI like ExDialer or something along those lines and when you click on a number, it still opens up to your normal dialer. So you'd still be sticking with the stock phone app for 90% of things.