It is very important to differentiate between a single QM photon in this case and classical light.
The two models work together perfectly, as the classical light (EM wave) emerges from the QM photon's herd.
Light as an EM wave does have amplitude, we call it intensity, and it changes with the number of photons it consists of.
A single photon does not have amplitude. Now this is not completely true, because as per QM, the electric field is described by probability amplitudes for each point in space. We can use probability amplitudes for certain field configurations. Whether we can use these probability amplitudes for single photons depends on the definiteness of the state of the single photon (in a defined state, we cannot use probability amplitudes for a single photon).