When part of a phone screen goes black, it typically indicates a hardware or software issue. The most common cause is physical damage to the screen, such as dropping the phone or applying too much pressure to the display. In these cases, the phone may need to be repaired or the screen replaced entirely. Another cause could be a software glitch or malfunction, which can usually be resolved by restarting the device or updating the software. However, if the issue persists, it may be necessary to reset the phone to its factory settings or seek assistance from a professional technician. In some rare cases, a black screen may also indicate a more serious hardware malfunction, such as a damaged logic board or video connector, which may require professional repair or replacement.