It depends on the time of year! Arizona (except the Navajo Nation) does not observe daylight saving time. This creates a unique situation:
During US daylight saving time (March to November): Los Angeles and Phoenix are the same time. Both show the same clock.
During US standard time (November to March): Phoenix is 1 hour ahead of Los Angeles. When it's 3:00 PM in LA, it's 4:00 PM in Phoenix.
Business hours work great year-round! During most of the year (DST), there's no difference. During winter, 9:00 AM - 5:00 PM LA is 10:00 AM - 6:00 PM Phoenix.
Many Californians have relocated to Phoenix for lower cost of living. The 1-hour flight makes the LA-Phoenix corridor one of the busiest domestic routes in the US.