Some very good clues here, and I appreciate the compositional problems to which others have referred. However, at the end I still felt a bit flat. Since we were given instructions on how to encode using the square, I expected the code phrase to give some sort of instruction about encoding other elements in the grid. When that didn't happen I wondered, as others have, whether I was missing something, but it seems not. Or does it?
Incidentally, for those who have been posting encoded text, the problem of encoding a pair of repeated letters is usually solved by interposing an X between the two before encoding. For an entertaining description of Playfair and many other codes, I recommend "The Code Book" by Simon Singh.