Dlp and LCD systems have been very high res for 10 years.

Those systems are projection systems. They project light that's explicitly focused on the surface of the resin using a lens.

The resolution in this device is decreased due to the resin tray being some distance away from the actual light-producing LCD (and its LED backlight), thanks to the touchscreen, glass, and resin tray that will all be between the LCD itself and the liquid resin. Since there's no lens, the light can't be focused directly onto the resin layer. Phone screens are, by nature, producing a diffuse light as opposed to a light that's focused at a point just above the screen. Your eyes are focusing on the surface of the LCD screen, but just a millimeter or two above the LCD (which is where the resin in this device will be located), you do not have nearly the same focus/resolution as on the physical LCD itself. Think of the way a flashlight's projected light gets blurrier and bigger as you move it away from the surface you're pointing it at.

You want proof of this? Put a nice photograph (or line art image) on your phone, and press your finger against the screen. Then look sideways at the place between your finger and the screen, and see just how blurry the image has become. Alternatively, take a piece of tracing paper or a tissue, and see how sharp the "projected" image is. Even flush against the glass surface of your phone screen, there's no sharpness/detail to the projected image, which is exactly what this entire system is relying on -- the projected image that your phone makes, just above its glass surface. It does NOT have the detail that you see when looking at the screen, because again, your eyes are focusing directly at the LCD screen's pixels.

Then you have the additional loss of resolution due to the fact that this system uses visible light, which takes longer to cure the resin, and will invariably "spread" to surrounding pixels that you don't want cured. The ambient light inside the chamber (due to the phone's screen) will slightly cured any wet resin that's around the desired "pixel" you're intending to cure. This will cause additional unwanted resin curing, thereby lowering the resolution.

You're dealing with a curing system that's not ideal. Despite the high resolution of phone screens, they weren't designed nor built to produce the kind of focused (via lens or laser) light used in current resin curing 3D printers. I'm incredibly skeptical of the detail you'll be able to achieve with a setup like this.