A cuspidor.
And I feel sorry for the guy or gal using the mic after you.

All seriousness aside though, I use crystallized ginger to "de-phlegm" my vocal cords.
Just pop a couple of pieces in your mouth and suck the living daylights out of them;
the ginger takes the phlegm coating off the cords.

Make sure to do it well before you go on stage.
There's nothing like hawking a few loogies in the middle of your big number.

Of course, if you're ill, and your vocal cords are simply protecting themselves with the coating, don't sing.

Seamus