As a PP said, you will have essentially two options when taking a taxi. If you tell the driver you want to go to the Magic Kingdom, they will probably take you to the TTC (taxis cannot drop folks off at the MK bus stop area). From there you have to take the ferry or monorail to get to the MK. Alternatively, you can ask the driver to take you to the Contemporary Resort and then you can walk to the MK. (I suppose you could actually ask to be taken to the Poly or GF and then take the monorail to MK as another option, but CR is probably faster because you're walking.)