I don't know a Vf of a hypothetical 'big' PC amber Rebel, I would guess 3.0 as a bottom (a 10% improvement). It may be possible to drive this hypothetical 'big' PC amber to 1.5 amps, producing 250 lumens. But efficiency really suffers.
The spectral half-width of the phosphor converter amber is 80 nanometers [565-645, I think], way better than direct amber [20 nanometers, 580-600] LEDS, and infinitely better than LPS.
Efficiency is lower than LPS, but if LPS is completely unacceptable in the marketplace, that efficiency advantage is moot.