Connecting iPhone to Samsung Sero TV with HDMI in portrait mode for both devices does not fill the Sero screen

I have a Samsung Sero TV. I connect my iPhone or iPad to the Sero with Lightening to HDMI cable. After selecting the input source on the Sero the iPhone image shows on the Sero screen. Both the Sero TV and the iPhone are in portrait mode. The iPhone appears as a small view in the middle of the Sero screen instead of filling up the entire screen. I have played unsuccessfully with the Picture settings on the Sero and have called Samsung customer support but the problem is still unresolved. All I want to achieve is to get the iPhone view on the Sero to fill the entire screen. Can someone please help?