Why the phone app is slienced??

[Deeo]

I didn't do any thing, but the phone app become slienced.... Now before I pick up a phone call, I need to unlock the lock screen and press notify on status bar....  It's very annoying.... Dose any one konw what's happened?? 

[_alexdon_]

You might have done it by mistake or a 3rd party app could be involved. You should be able to enable notifications normally for the phone app by tapping on the app then press the slider.

EDIT: I have noticed that there is no slider for the app, so a 3rd party sounds more likely. Can you let us know @Deeo?