is it possible to use my phone's wired headphones (which have only one output jack) to my laptop and use it as both earphones and mic? Which normally require 2 separate jacks
Yes it may be possible but with out knowing the headphone it's hard to tell.
Assuming your headphone is both a mic and speakers, and the other end is using either a jack or a mini-jack, you'll need to see how many black lines are around the connector. 1, 2 or 3. In music, 1 means mono and 2 stereo. The third is for 'other', in this instance most likely a microphone.
This image may help (although not your device)
As per our comments and keep all relevant data in the main answer, you will need a splitter or adapter - please see http://www.meelec.com/MEElectronics_Skype_Adapter_for_PC_p/adptr-skype-22in-35.htm for an example. If this link fails, then try a search engine for a term similar to "trrs adapter" or "trrs skype adapter".
You might need an adapter like one of these, which can convert a TRRS type headset to two separate audio and microphone plugs.