Q: Whatsapp crashed and phone restarting (iphone 6+)

Greetings 4lysha,

Welcome to the Apple Support Communities!

I understand that you have an application that you downloaded from the App Store that unexpectedly quits and after it does this, your iPhone also resets. There are two different articles that I would suggest reading over and working though in this situation. 

First I would recommend troubleshooting WhatsApp to isolate the issue. To do this, please follow the instructions located in the attached article. 

If an app you installed unexpectedly quits, stops responding, or won’t open - Apple Support

If the issue continues after troubleshooting WhatsApp, please follow the instructions located in the next attached article. 

If your iOS device restarts, displays the Apple logo, or powers off while you're using it - Apple Support

Cheers,

Joe