iPhone black screen may be caused by dropping your iPhone, spilling water on it, updating an app, malware, bad firmware, jailbreak, etc.
To fix the problem, first start by fully charging your iPhone to rule out any battery issue.
If the problem persists, then restore your iPhone to factory settings via iTunes but this also leads to iPhone data loss. If you do not have a backup, consider Stellar Data Recovery for iPhone to recover photos, videos, music, messages, chats, contacts, etc. from the device. Read more
