So you want a device with a 13" or larger screen that you can fit in your pocket? Good luck with that.
Any device is a compromise.
Perhaps a device with a 7 inch screen and a small bezel that has detachable keyboard and operates through a Bluetooth headset for the phone function.
Or maybe a larger tablet that has your cellular/data connection, combined with a dedicated Bluetooth telephone handset.
It is just silly to say things can't get any better. In a couple of years somebody is going to come along with something that we have not foreseen, and will wonder how we ever lived without it.