How can i replace a electret mic input with headphone output as input
The 90mW into 32 ohms from the headphones output of your mobile is 1.7V (RMS?).
The output of your voice from an electret mic (conversation level at a distance of 10cm) is only 10mV. So you must attenuate the headphones signal 1.7V/10mV= to 1/170.

90mW into 32 ohm headphones is VERY loud. 100mV from an electret mic is also VERY loud. Then attenuate to 1.7V/100mV= 1/17th.