If a progress bar has not moved for at least one hour, connect the iPhone to a Mac or PC, enter recovery mode, and choose Update first. Restore erases the phone, so use it only after the update path fails and you have checked your backup.
An Apple logo during an update or data transfer can remain on screen for a long time. Note the progress-bar position and wait at least one hour before treating it as stuck. Disconnecting power during an active update can make the startup problem worse.
Decide whether it is actually frozen
Keep the phone on reliable power. If the bar advances, even slowly, continue waiting. Move to recovery only when the bar has not moved for at least an hour, the logo restarts repeatedly, or startup never reaches the Lock Screen. Stop and seek service if there is impact damage, liquid exposure, swelling, or excessive heat.
Reinstall iOS without erasing first
Update the Mac or Windows PC, then connect with a data-capable cable. Open Finder on a current Mac or Apple Devices/iTunes on Windows. Use the button sequence for the iPhone model and keep holding until the recovery-mode cable-and-computer screen appears.
When the computer offers Update or Restore, choose Update. Update attempts to reinstall iOS while retaining personal data. Keep the computer online and do not disconnect the cable. If the download takes more than 15 minutes and the phone exits recovery mode, allow the download to finish, then enter recovery mode again.
Understand the Restore decision
Restore erases the device and installs iOS again. Before choosing it, verify the date of an iCloud or computer backup and that you can sign in to the Apple Account used on the phone. Restore does not remove Activation Lock and should never be advertised as an ownership bypass.
Save any error number shown by Finder, Apple Devices, or iTunes. Try a direct USB port and another known-good cable if communication fails. Repeated failure at the same point, inability to enter recovery mode, or broken buttons is a reason to contact Apple Support with the exact error and hardware history.
Primary sources
Interfaces and policies change. We recheck the steps above against these sources and show the verification date at the top of the guide.