Digital input to mobile phone headset port?
Apparently you have a audio signal with 3.3 Volt peak to peak amplitude and want to couple that into a "microphone" input of some other audio device.  Microphone inputs are meant to take the very small signals produced by microphones.  These are often 1 mV or less, with peaks maybe a few mV in normal operation, although this depends a lot on the microphone.  

For starters, you probably want to attenuate your input signal by at least 1000 in voltage.  That may still be a bit high, but most microphone inputs can probably handle that.  You will have to experiment.  Maybe you need a attenuation of 3000 or 5000 so that you set the volume control near the middle of its range when listening.  A simple start would be:



That will attenuate by about 2000 in voltage.  Note the capacitor to AC couple the signal, which removes the DC bias of the input signal.