It also looks like it might have crown rot in the crown. Be sure to not get any water on the leaf, except to maybe wipe it down and do the treatment suggested above. You might be able to bring it back even if it loses the one last leaf, as the roots look pretty good. Sometimes keeping the roots misted and the top ones exposed will allow it to start a basal keiki and basically start over. The Phals are basically pretty tough. Spray it enough that those top roots stay green and plump and see how it does!