Except Python 2 isn't going to be "phased out". Just support from Guido and company will end. Alternate support will continue on with fully compatible py2 implementations such as PyPy and pyston. "python" will still point to python2 on Linux distributions and Python distributions such as anaconda will still have the established, mature, fully functional python2 suite available.
No actually phasing out of Python 2 has already begun.
Several libs today are Python 3 only. Many, many more are not going to pay the cost of supporting Python2 and drop it in next few years.
Unless you are retiring next couple years or live with head in sand, any new code you write should either by python2-3 compatible (it's not hard at all, do it all day every day) or Python 3 only.