Is The Phantom Menace the first major reboot/legacy sequel (technically prequel) of a big franchise? It is actually way ahead of its time in that regard considering how many reboots have come about in more recent years.
shareI don't think it qualifies as a "reboot," because reboots are usually set up as the same story but with newer actors/characters in similar or the same roles as the original story. Plus, the original story is tweaked to suit the writers of the present time, rather than how the story was originally told. This story is very, very different from "A New Hope."
Unfortunately, Lucas unintentionally set a bad precedent for Hollywood years down the line when they went nuts about making "prequels" and "reboots" for everything after 2013. They saw how much money the Star Wars Prequel Trilogy raked in (despite the complaints) and wanted to rake in that dough too, not realizing that you have to be careful when making a backstory for an older work. That's how we ended up with prequels that are inconsistent with the later TV shows and movies we'd all grown to love in the past.