A digitizer is separate from the display screen on all modern mobile devices, and a malfunctioning touch screen will always require the replacement of the digitizer component.
While the digitizer is typically integrated with the display screen on modern mobile devices, it is not always and can sometimes be part of a combined display assembly or separted from the display assembly. In some cases, malfunctioning touch functionality does not necessarily mean that the digitizer is faulty; it could be due to software issues or other hardware problems.