Is that true? How does that integrate when you have X pixels shared by two eyes vs. X/2 pixels for each eye above the flicker fusion threshold?
Not sure what you are referring to when you say "flicker fusion threshold." AFAIK, there's no blinking or alternating light with this phone. It's left and right images interlaced vertically, so even vertical stripes are from one image, and odd vertical strips are from the other. And unlike traditional "interlaced" signal, all stripes are on because of the LCD progressive scanning. Add the parallax barrier to make sure the proper vertical stripe lands on the proper eye. No flicker involved.
The parallax barrier is rigid and unmoving. The barrier always appears vertical relative to the orientation of the phone. In the sweet spot, a given pixel is only seen by the left eye, and by definition, the right eye sees the black of the barrier. The next pixel over is seen by the right eye, and the left sees the black of the barrier.
So each eye is only getting half of the resulting picture, and the brain puts it together. But the parallax barrier is not invisible; the black stripe is something we perceive as well. So, all of this data is present in the "video input" to our brain, so we end up perceiving a fully assembled image with depth but also with vertical stripes.
Those vertical stripes effectively reduce the resolution. Just like at the eye doctor: it's easier to identify the letter with both eyes open than with just one. Our ability to resolve detail is actually diminished by the parallax barrier.
In 3D mode, the UI elements (share, delete, etc) appear at the level of the screen because they are zero-parallax images. The problem is, they reside underneath the parallax barrier, so their resolution is unnecessarily cut by half. A lenticular array would solve this problem by not diverting the UI pixels to left and right eyes.
It should be quite easy to tell that the UI buttons look fuzzier in 3D viewing mode than in 2D mode. If they look the same to you, then I'm going to chalk it up to the same reason some people don't see the screen door effect of PenTile screens
The brain just does TOO good a job blending.