Why does my phone turn off constantly?
My phone constantly turns off, and I don't know the reason why.
iPhone 5, iOS 6.1
Lots of possible reasons such as corrupted data or settings, a bad app, malfunctioning hardware, water damage, etc. Previous hacking/jailbreaking (or attempted hacking) which can't be removed is a common and non-fixable cause.
Restore the phone, first using a backup, and if needed as a new phone, without using a backup. If restoring as new doesn't help, you need warranty service from Apple or whoever provides this in your country.