A lock screen stops anyone casually opening your phone from seeing client data. For the data itself to be unreadable even if extracted, ask about turning on encryption.
Google Sheets backup
Auto-backup to Google Sheets
Off — data is saved on this device only.
One-time setup (≈3 minutes)
Go to sheets.new to make a blank Google Sheet. Name it anything.
In the menu: Extensions → Apps Script.
Delete whatever's there, then paste this in and change the secret word on the first line:
Click Deploy → New deployment. Choose type Web app. Set Execute as: Me and Who has access: Anyone. Click Deploy and authorise (it's your own script — accept the Google prompts).
Copy the Web app URL it gives you, paste it above, type the same secret word, and turn the toggle on.
Tap Test connection, then Back up now. Your Sheet will fill with Shifts, Clients and Settings tabs.
Your data always saves on this phone first and syncs to the Sheet in the background, so nothing is lost even if you're offline.
Clients
Local backup file
Download a one-off backup file (e.g. to iCloud Drive) in addition to the live Google Sheets sync.