I don't see the point in phasing out the Slim PS4 model. You can have a Slim PS4 and a Portable PS4 at the same time. Thay're not the same thing. (Although I don't think there will be a portable PS4 and I'll get to that in a sec)
It doesn't hurt Sony to have both PS4 Slim and Pro because they essentially use the same components, while giving customers more variety in price point. Cutting out the Slim would be a dumb decision imo.
As for PS4 Portable, I don't think technology exists that would make this affordable enough to be a good idea at this time.