TANGERANG, Indonesia/TAIPEI — At 50 specialized stations, technicians in cleanroom suits meticulously assemble smartphone circuit boards, speakers, cameras, displays and batteries into casings in a seamless process capable of completing a phone in just 500 seconds, or around eight minutes.

The cleanroom in Tangerang, an hour’s drive from Jakarta, started out a decade ago as a small plant owned by Chinese smartphone maker Oppo.