First thing you need to do is open the settings App, this is by default, on the first page of your iPhone.
Once your in the settings app, scroll down to the general tab and press it to open another screen.
Next you need to press the Accessibility tab. This will open another screen.
Lastly you need to scroll down to the tab where it says "LED flash for alerts" and switch it to the on position.
And that's it! Now you will have flash alerts for calls and texts. NoteThe only thing is that the phone needs to be Facedown in order see the flash, Otherwise you can't see it.