Updated
Quick fix
Restart the phone, install updates, and make sure at least a few gigabytes of storage are free. If one app freezes, update or reinstall it. A full reset is the last resort, after a backup.
Step by step
Restart
A restart clears memory and stuck processes. If the phone is frozen, use the manufacturer’s force-restart button combination (search your exact model).
Install updates
Update the system in Settings and update your apps from the App Store or Google Play.
Free up storage
Phones slow down when storage is nearly full. See storage full.
Find the problem app
If slowdowns happen in one app, update it, clear its cache (Android) or delete and reinstall it.
Remove apps you don’t use
Fewer apps means fewer things running in the background.
Check battery health
A worn battery can cause some phones to slow down to protect themselves. See battery drain.
Reset as a last resort
If nothing else works, back up first, then reset the phone to factory settings and restore your backup.