At one end of the wire is a 3.5 mm Jack plug. On the other end of the wire is presumably a glass LED.
When connected to the phone, nothing happens. The LED does not start to glow.
Also, this wire doesn’t work as a microphone. It’s also not an earpiece.
What is it for?
Audio jack ir blaster adapters for phones used to be common. You can still buy them on eBay.
Audio is voltage changes which can be set to drive an ir led. You use an app that outputs audio that matches the ir signal protocol.