iPhone 6 automatically switch off in Every 5 minutes

@mrssavitadevi Is there any chance that "switch off" is a reboot? When it turns off, does it automatically start back up immediately? And is it possible that the timer interval, should you actually measure it, comes out to be closer to three minutes?

If both of those are true, then chances are you are experiencing what's called a boot loop. Essentially the phone detects an error and tries to reboot the phone, but once the phone has restarted it sees the error again and once again tries to reboot the phone. Since it's basically stupid, it can't know that doing it over and over again isn't going to help so it does it anyway.

The three minute interval is because that's the time between when the phone scans its sensors, so that's a pretty good indication you're in a boot loop due to that reboot cycle, which is called a kernel panic. @flannelist has written an excellent guide to those and it shows you how to find and interpret the log files that get saved when it happens.

iPhone Kernel Panics - iFixit

So your job now is to go into the phone, locate the newest panic log and post the first page of it to your question. A screen shot or cut an paste are both fine.

Adding images to an existing question - iFixit Repair Guide

Once we have that we should be able to pin down pretty much exactly what's wrong with your phone and how to fix it.