Why is my iphone turn blue screen frequently?

Standard troubleshooting steps as outllined in the manual are restart, reset, restore, and restore as new. Have you powered off the device and turned it back on? Have you done a reset as outlined below?

Close all open apps by double-tapping the home button, then swiping up and off the screen with the app window (not the smaller icon).

Reset your device: hold down the home button along with the sleep/wake button until the screen goes black and you see the Apple, then let go. (No data loss)

Did you perform all of the troubleshooting steps that were provided? If you performed all of those steps, including the restore as new, then you need to make an appointment at the Genius Bar or Authorized Apple Service Provider, depending on where you live, and have the hardware checked.

IF you are covered by the warranty you can. Call apple support and they will run a diagnostic test with it. Let them make an appointment for you as well if you like to go to genius bar. If you are covered by any warranty, you can just ask for pay per incident service which will cover you for a month