When you sign up for iCloud, you got 5 GB of free storage. iCloud automatically backs up your iPhone over Wi-Fi every day while it's t...
When you sign up for iCloud, you got 5 GB of free storage. iCloud
automatically backs up your iPhone over Wi-Fi every day while it's
turned on, locked, and connected to a power source. Your iCloud backup
includes data and settings stored on your iPhone, such as contacts,
notes, calenars, bookmarks, mail messages, photo stream, etc. To decide
what are backed up from your iPhone, iPad or iPod : navigate to your
iPhone, go Setting >> iCloud, then turn on iCloud backup.

Warning: Since you have to erase all content on your iPhone before recovering contacts from your iCloud, the process could also erase some new and important data on your devices.
How to restore your contacts with iCloud
When you set up a new iOS device or need to restore contacts on one you already have, your iCloud backup makes it easy.- Make sure you have the latest iOS version on your iPhone, iPad or iPod. You can go to Settings > General > Software Update and have a check. If a newer version of iOS is available, follow the onscreen instructions to download and install it.
- Clean up your iDevice. Go to Settings > General > Reset, then tap “Erase all content and settings.”
- In the Setup Assistant, proceed to “Set up your device,” tap Restore from a Backup, then sign in to iCloud.
- Proceed to “Choose backup,” then choose from a list which contains your previous contacts backup in iCloud.
Warning: Since you have to erase all content on your iPhone before recovering contacts from your iCloud, the process could also erase some new and important data on your devices.

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