Hi, Thomas,
If you are after a true rotation of the text, create it in a text box and from the Wrap Inspector uncheck “Object causes wrap.” Next, hold Command and select the text box. You’ll see the curved arrow indicating rotation. Rotate text to vertical. Then go to your table and hit “Return” enough times to enlarge the cell enough to fit your text into. Now drag the text box into the table. However, if you now type into that same cell, it will overwrite the text box with your vertical text.
Good luck,
Walt