We never wipe a phone during a repair. But hardware can fail at any time, and a fresh back-up is the difference between "annoying" and "lost-forever" if it does. Here's the 5-minute version.

Option 1: iCloud (easiest)

Plug your phone in to charge
Connect to Wi-Fi
Settings → [your name] → iCloud → iCloud Backup → tap Back Up Now
Wait — it tells you when it's done

Apple gives you 5GB free, which is enough for a basic back-up. If you've got lots of photos you'll need iCloud+ (£0.99/mo for 50GB) or use option 2 below.

Option 2: Your computer (no cloud subscription)

Plug your iPhone into a Mac or PC with a Lightning/USB-C cable
Open Finder (Mac) or Apple Devices (PC)
Select your phone, click Back Up Now
Tick "Encrypt local backup" if you want passwords + health data included

What gets backed up

App data, settings, messages, call history, ringtones, home-screen layout, health data (if encrypted). Photos go separately if you have iCloud Photos on (which you should).

What to check after

Settings → [your name] → iCloud → iCloud Backup. The "Last Successful Backup" date should be today. If it's older than a week, the back-up didn't run — usually a storage issue.