My BLU phone was rebooting all the time.
I noticed the battery was moving around in the back of the phone.
I am a swimmer and I use silicone ear plugs to keep the water out of my ears.
You can buy these at any pharmacy.
https://www.cvs.com/shop/cvs-health-ultr...
I stuck one of these ear plugs between the battery and my case.
And the battery stopped moving around inside the phone case.
And that solved the problem.
Uncle G
PS: Also make sure your battery isn't dead.
That is the first thing I checked; wasn't that.