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
deleted by creator
I also have some that look just like that, and it’s the blaster bit because it stickies directly to the face of the device to control buried in a cabinet. The led is shielded and stuck directly next to the other devices receiver.
Suffice it to say, there’s no standard. And if the OP doesn’t know what it is, they probably don’t have the rest of it to make it do anything cool. Last I checked they were about $5 on Amazon for the whole getup, so I’d just e-waste that.