I have updated my iPhone 6 plus in to ios 9.2. Now sometimes my iphone thinks that I'm plugged my headphone. So what is the reason?

Hi chamarafrommawathagama,

Thanks for using the Apple Support Communities! I'm sorry to hear you are having these issues with your iPhone. I'm a bit unclear on exactly the behavior you are describing, but if you having issues with your headphones (or the phone behaves like the headphones are plugged in when they are not), you may find the troubleshooting steps outlined in the following article helpful:

If your headset isn't working - Apple Support

Cheers