Why is my phone blank but still working?

My phone is severely cracked and shows the whole top part of the phone (camera and speaker section), so I can see if the backlight is on or not. When I turned on my phone, the screen was blank and the blacklight was on, then the backlight just turned off and my screen was obviously still blank. My phone still vibrates as if it was turning on again after charging and also makes the noise when I plug in the charger, but about that noise, it makes it continuously like the charger was going in and out. Lastly, when I had messaged my friend and told her to call my phone, it didn't ring, and I wasn't getting any notifications either. What should I do?