That's exactly what I mean - and what I wrote in the post you replied to.
If I connect my X-box to the Composite AV inputs (Red, White and Yellow RCA) I get sound and vision; if I connect my iPhone or other audio source to the AV sound ports without a video connection (Red and White RCA only) I get nothing and can't even select the AV channel. This is true of my TV and clearly the one used by the OP. I have also had exactly the same experience with Composite AV connections on other devices - if there is no video connection the device will not recognise that selection.