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?
It’s part of an IR Blaster setup. That looks like the “blaster”, aka the IR LED Transmitter. Most receivers have multiple ones to catch reflections and such