Why my iphone 6 screen freezes frequently?

 have iphone 6 running iOS version 9.3.1

Phone screen is freezing frequently. I can see the screen but touch does not work. If I lock the phone by pressing Power button, after that it works for few minutes. But every now & then it freezes. It happens with all applications even on Home screen. Not sure what causing this.
Appreciate  if anyone can help !
iPhone 6, iOS 9.3.1
Has invited:

howapple - hello

Favor from: apple

Try to reset your device. This won't delete your data stored on this device.
  1. Press and hold the Sleep/Wake button
  2. Press and hold on the Home button
  3. Keep holding both buttons until the display turns off and back on with Apple logo on it.

Alternatively, you may go to Settings - General - Reset - Reset All Settings

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