Solution Steps

1. iCloud backup: Settings → [Your Name] → iCloud → iCloud Backup → Back Up Now.
2. Ensure connected to Wi-Fi and plugged into power.
3. Computer backup (Mac): Connect iPhone → Open Finder → Select iPhone → Back Up Now.
4. Computer backup (Windows): Connect iPhone → Open iTunes → Click iPhone icon → Summary → Back Up Now.
5. Check backup size: Settings → iCloud → Manage Storage → Backups.
6. Enable automatic backups: Settings → iCloud → iCloud Backup → Toggle on.