Phone Glitch- How do I restart?

I got a phone call earlier and ever since it has made my phone glitch. I tried to accept the call and that is when it started to freeze. The name and regular active phone-call screen was just gray. I could not hear the person and eventually it went back to my normal home screen. Now I can swipe between pages but I cannot open any actual apps. My screen locked by itself after several hours of just being on. I was able to swipe back into my phone but it still won't open apps for me. I now have the flashlight turned on and brightness all the way up to run down the battery. How could I turn it off in the meantime?! (Already tried holding down the volume/lock simultaneously and nothing)