All sunxi devices use LiveSuit as a default flasher and updater for retail customer and PhoenixCard or PhoenixUSB for flashing when devices are manufactured. LiveSuit/Phoenix protocol and data are closed-source standrad used by many companies and devices.
Please note that PhoenixSuit is actually LiveSuit2.0. There are different platform's PhoenixSuit
Please refer to the Livesuit/PhoenixSuit Installation Guide
Assuming you are going to use lubuntu-desktop-12.10 v1.05
$wget http://dl.cubieboard.org/software/a20-cubieboard/lubuntu/cb-a20-lubuntu-12.10-v1.05.img.gz $gzip -d cb-a20-lubuntu-12.10-v1.05.img.gz
Run Livesuit, select the image we just extract
Press the FEL key when power up(the FEL key is the one under the USB OTG port), The CPU automatically enters FEL mode. Livesuit will start to write the image to Nand on board.