If you experienced a global blurry rendering on your screen when you use DirectX11 on your Windows Phone 8, you probably fails a thing :
The swapchain size must be the screen size (means portrait), not the landscape size.
So :
swapChainDesc.Width = 800;//
swapChainDesc.Height = 480; // blurry rendering !
swapChainDesc.Width = 480;//
swapChainDesc.Height = 800; // perfect rendering !
That’s all, take care !1