Glass vs. LCD
The way to know if your device needs the glass replaced or the LCD Replaced is simple in most cases.
If you have an iPhone that hasn't ever had a screen replaced and the display and touch work perfectly with the cracks on the glass than a glass replacement is all you need.
If you have had the screen replaced previously chances are very good that you had an aftermarket screen installed on your device. Almost all types of aftermarket screens are manufactured in a way that makes it so the glass cannot be replaced, in which case you will need a new display.
You will also need a new display if you have issues with it or the touch.
First Let me define a few terms:
LCD- Stands for Liquid Crystal Display
LED- Light-Emitting Diode
OLED-Organic Light-Emitting Diode
AMOLED- Active Matrix Organic Light Emitting Diode
Digitizer - Is simply the Layer on the display that responds to touch.
There are basically three classes of LCD's. One is a (LED)back-light driven display or in other words a display that needs a series of LED lights in order for you to see what the display is showing; this would be considered a regular LCD, The second is an OLED Display which is easiest described as an organic layered screen that reacts to different amounts of electricity. Note;it takes less electricity to power a OLED than an LCD.
The Third is an AMOLED Display which is similar to the OLED Display yet much better.
This is why Samsung S and Note series phones have always had clearer and cleaner displays vs the iPhone LCD.
The iPhone X Uses a Display manufactured by Samsung. Samsung is currently the only company with the manufacturing power and technology to make these displays.