Before a phone repair
A repair shop may ask for your passcode to test the phone. That gives a stranger everything on it, for days.
Before you hand it over
Back up the phone. Sign out of anything you can. Move private photos, passwords and documents into a vault: the passcode doesn't open it.
For anything very sensitive
Use travel mode: back the vault up, check the backup with your recovery words, and take the vault off the phone. Restore it when you get the phone back.
When you get it back
Change your phone's passcode, check your accounts, and open your vault to make sure everything is there.
Features that help
Take back your privacy.
Free to download. No account. Your files never leave your phone unless you choose.