Could you use polarization filters to make a privacy screen? I remember seeing that brusspup video where the polarization filter on the monitor was removed and put it in his glasses, causing only the wearer to see the screen.
(, and)
I was thinking, would another polarization filter set on top of a phone screen to re-twist the polarized light and another in glasses achieve a display that others see only white, while the wearer can see the actual contents?
If not this idea, is there any possible way?
 A: Putting a polarization filter of any kind (linear or circular) at any orientation onto your iPhone screen will never be able to turn its display from normal-looking to all-white. Look at it this way: If you have a display on your iPhone screen that has black areas (say, black text on a white screen), then that means that no light photons at all are coming out of those black areas. No sort of polarizer at any orientation is going to be able to turn those black areas to white since there is nothing for them to work with - there is no light energy at all emerging from those areas so putting a polarization filter over those areas has no effect. Black remains black. 
It you want your iPhone screen to look all-white to others, then the only way is to take out one of the polarization filters of your iPhone's LCD display just like the people in your linked video removed a polarization filter from their LCD monitor.
You might also want to check out this other question where the effect of removing the polarization filter from an LCD screen is discussed: What happens if you remove the polarization filter from a computer monitor?
