The iPhone is capable of many tasks, such as making calls, surfing the web, and playing music, amongst many others. Just as the iPod was popular, many users use their iPhones as their primary media player. If you wish to use your iPhone to play music through your home stereo, add a common 1/8" to stereo RCA cable to connect them easily.
Plug the 1/8" end of your 1/8" to stereo RCA cable into your iPhone's headphone jack.
Plug the RCA outputs of the cable into the RCA inputs on your stereo. Many stereos have both output RCA ports and input ports, so make sure it is in fact the input ports that you are using.
Set your stereo to the corresponding input setting for the RCA ports that you used.
Press play on your iPhone to test the output. If you cannot hear anything, check to see if the stereo and iPhone are properly connected and that your stereo is on the right input.