Amplifier the smartphone headphone port voltage

Feed the headphones output from the phone into the input of a more powerful amplifier. Then the IR LEDs might be destroyed.

 

If you have an external 5V power supply or battery then a single transistor can amplify the 3.5V to 5V.

 

What will you use to receive the IR signal? If it's a gizmo with an irDA port then the signal you send to it needs to be a digitally coded one, not the analogue one available at the headphone output of your phone.

 

The plug for the headphones has 3 connections but you do not show which 2 connections you used.
The tip and ring are Left and Right channels and the sleeve is the ground for both channels.
An LED works from DC current but the audio has no DC, it has AC.

The single transistor amplifier I mentioned is powered from the external 5V. The audio from the headphone jack on the phone gives AC signals to the transistor. The transistor amplifies the signals.

 

IR LEDs are typically around 1.5V, not 5V.

Bob

 

He does not show which two pins of a 3-wires stereo plug he has the IR LEDs connected to and does not show a schematic to show if they are connected with opposite phase. No current-limiting resistor is shown so maybe they are already burned out.