Why when I turn my iPhone 6 plus sideways does the screen not turn sideways?

[iMore Question]

The screen does not turn sideways when the phone is turned sideways

 

[Spencerdl]

The screen does not turn sideways when the phone is turned sideways

If you are referring to the home screen, the 6 Plus must be in "standard effect mode" to turn sideways. Settings > Display & Brightness > Display Zoom > "Standard"

 

[JOSH_WH1TE]

If you are referring to the home screen, the 6 Plus must be in "standard effect mode" to turn sideways. Settings > Display & Brightness > Display Zoom > "Standard"

Another thing to check is that rotation lock is turned off.
To do that swipe up into control centre and the toggle will be on the right hand side.