Powerpoint 2010

You cannot really isolate and animate it within the text box unless it is a full bullet or paragraph.

But there's a workaround -- follow these steps:

Create a new text box which contains just the word or a short phrase that you want animated. Match it in formatting (text color, size, font type, etc.) to the same as the text in the larger text box.

In the larger text box, remove that word or phrase from the rest of the text, and compensate for the removed space with empty spaces using the spacebar.

Now place the word or phrase text box right over the existing box, in the position that you want it to be. You might have to tweak it by repositioning or resizing the box.

Now animate the text box that contains the word or phrase.

It will help to know that you can hold your ctrl key down and use the arrows on your keyboard to move the text box 1 pixel at a time.