Welcome to AC
What are you trying to do with the phone? Cast the display onto a TV? That can be accomplished using the screen mirroring feature on the phone (this is definitely in settings) which I believe works with DLNA compatible TVs/computer displays. Other than that, you'd have to use a casting service like Chromecast, but you'd also need the according dongle for your TV.
I'm trying to watch it on my tv. I purchased cable that hooks into headphone jack and turns into rca cables I've hooked it up and turn tv on but am not able to get it to send signal to tv
I don't think it works that way. The phone doesn't use the same standards for displaying the screen as some other devices would, so the only way to get it to work would be to use the methods I mentioned above.