I take it this is going into AV In (2) and not headphone out (3) which is not an input?
Your connecting cable needs to be a four-pole, wired thus:-
But I would guess you are plugging in a three-pole audio cable? So you need to get from three-pole to four-pole, probably with a three pole female to two male phonos cable, and then a three female phonos to four pole, like the one in the picture above, and then use just the L and the R female phonos.
Though it may anyway well be that the TV detects no input video, and so gives no signal, not even from the sound channels.
But you have other connection options than just analogue audio; see this article for a full rundown on alternative approaches:-
https://uk.pcmag.com/how-to/40528/how-to-connect-your-iphone-or-ipad-to-your-tv
