Are you sure the roots are rotting? If it was dried out then it might be blasting buds for that reason. It's best not to disturb the roots during flowering, but it seems you've unpotted it now. I would go ahead and repot it with the spag just don't pack it in there super tight. When I water my phals I dunk them up to the top of the pot and let them sit for a little while to get nice and wet. Then I just let it dry out over the week and repeat once a week.