A VGA signal is composed of a Red,Green,Blue and also Horizontal and Vertical Sync information. You cannot simply do a VGA to Component or Composite within a cable. The signal types are different.
The VGA to RGB Cable you have is meant for inputting Component video in to a device that will accept them through the device’s VGA input port. This type of use can be found in some projectors as an auxiliary type input, but by no means is this a VGA signal. VGA to RGB cables are for proprietary purposes, I know its kinda confusing!
If you must use a Component input you will need a scan converter.iPhone 5, VGA Dongle
The iPhone 5 Will output 1366X768 or 1920x1080, or 4:3 resolutions (Letterboxed). It really depends on the highest resolution the you display will accept (EDID information),
Please note that you can't watch DRM content ( purchased through iTunes) using the VGA output you must use the HDMI adapter.