No, it wouldn't work. The Phantom has the controller in-between the function key row and the number key row, so you would be cutting it away.
If you go full tenkeyless, you would have more options for cases.
An alternative would be to get on the Red Scarf II GH/DT Edition group order when it opens. It is like a Poker + numeric keypad on the right without any spacing, but you could map it any way you like, so you could get a layout like yours except for a full key's horizontal spacing between the arrow keys and the main keys.
Other features include backlighting and compatibility with Hasu's popular TMK firmware.