Camera LED in phones - PWM or analog current controlled?
PWM and Linear analog current regulators are very inefficient with a wide input battery voltage range >25%.  A Boost regulator is preferred with at least 2 LEDs. A boost reg. is essentially the best of both PWM and reactive LC filtering to regulate the boost energy with some variations in current and time limits.

Each mobile phone may have a different solution.

Here is one offered by a product marketing manager at ON Semi reported in EE Times on 06.12.08.


  An inductive step-up converter with high power driving circuit of 4.5 W is capable to power two LEDs in series with a driving current of 500mA.





  Figure 6. A 4.5W power-flash driver with internal switch and time-out protection