24th century style Phasers in use when "The Cage" used lasers.
That was Roddenberry's own retcon. He coined the term "phaser" because he decided it had been a mistake to call the weapons "lasers." Even in 1964, only four years after the laser was invented, it was well-enough understood that people would've known "The Cage"'s portrayal was wrong. So he abandoned the "laser" terminology and replaced it with a made-up weapon name. He would've wholeheartedly approved of a prequel ignoring the use of "laser" in the first pilot. He wouldn't have wanted it to perpetuate something he himself considered a mistake.
Anyway, let's not turn this thread into yet another ENT-bashing thread. Surely all of this has been rehashed a million times already, and it's not a suitable topic for the Trek Literature forum.