I am using my mobile phone as a modem throught Wi-Fi tethering in Android OS. How can I see the port number to which my modem is listening? i have used "ipconfig" in cmd to see its defalt gateway but now I need to see its associated port number.

My bet is your phone is using its WiFi hotspot rather than a tether. As such the ports are more than one. Just like when you use a WiFi router or hotspot you get to use 65,535 ports. I know some call this tethering but as an old router coder, I would not call it that.

You can use your phone as an internet gateway (tethering) or a wifi hot-spot (router and WAP). I've used my phone for both in the past (until AT&T said I'd lose my unlimited data plan doing that). The tethering option is good when you just want to use your phone like any internet modem. The hot-spot option allows others to use the phone to get on the internet as well. I used both as a teaching tool when giving classes in internet/cell-phone technology to AT&T techs a few years ago.