i have accidentally deleted icloud icone, how to get back?

There is no iCloud icon on an iPhone. Perhaps you meant iCloud Drive? If so, be aware that iOS 11 replaced the iCloud Drive app with the Files app.

If you are still running iOS 10 and deleted the iCloud Drive app, see the following from https://support.apple.com/en-us/HT204221

Restore a built-in app that you removed

1. On your iOS device, go to the App Store.
2. Search for the app. Make sure that you use the exact name of the app. Find the correct name of built-in apps.
3. Tap to restore the app.
4. Wait for the app to restore, then open it from your Home screen.