I'm trying to connect my phone to my pc so that I can input and output sound to it. I have a 3.5mm jack splitter with headphone and mic connections. Then I have the headphone port connected to the mic port on my pc and that works for hearing the phones audio. However when the adaptor mic port is connected to the speaker jack on my pc there is just a crackle noise picked up by recordings on the phone.
The output of the pc is going to be at a voltage level (line level) that is way higher than the phone is expecting (mic level). You need an 'attenuator' between the pc and the phone that will drop the level by between 30dB and 40dB. If you are savvy with electronics, you can build an attenuator with a few resistors.