You can use the arrow keys to move the cell selection around.
You can jump to adjacent cells with the arrow keys by pressing “out of the text” while you edit: When the text editing cursor is at the left end of the text, pressing the left arrow key jumps to the cell to the left; similarly, when the cursor is at the rightmost end of the text, pressing the right arrow key jumps to the next cell to the right. You can always immediately jump away with the Tab key (or Shift (⇧)-Tab).