LED headlight eating away at power output of USB charger
A hub dynamo is typically rated at 6V/500mA, and most lights will use all of that. Modern LEDs give you a lot more light from that power, but it's still nowhere near as much as the high powered battery lights you can buy (so if the manufacturers could get more power into the lights they would probably offer it as an option).

So the extra power you're getting into your phone comes from the "sometimes you can get more power" part of the dynamo specification, not the guaranteed part. In reality most dynamos will go well over 6V once you're moving at a reasonable speed, and the regulator you haven't installed is mostly to prevent incandescent lamps from burning out when that happens. With LEDs a better regulator has to be built into the lights because LEDs are more sensitive to the exact voltage/current they get.

This answer gives more links to information about how much power you can get.