Catalyzes the decarboxylation of 4'-phosphopantothenoylcysteine to 4'-phosphopantetheine. H(+) + N-[(R)-4-phosphopantothenoyl]-L-cysteine = (R)-4'-phosphopantetheine + CO2 Binds 1 FMN per subunit. Cofactor biosynthesis; coenzyme A biosynthesis; CoA from (R)-pantothenate: step 3/5. Belongs to the HFCD (homooligomeric flavin containing Cys decarboxylase) superfamily.