Why would you need 6v for a phone? I got feeling this was pulled out of his ass. Everything works on sub 2V there if I am not gravely wrong (not sure for the light source for the display)
You don't. I'd bet most of the voltage rails on a modern phone are 1.8V and 3.3V. Then the display backlight usually uses a constant-current regulator, and you'll probably have some oddball low voltages for the CPU core and other various things. Given Ohm's law you can generate all that using DC-to-DC converters.