Your basic plan is good, but be aware that if you arrive in PHX at 5pm on a Friday nite in June you will be contending with TONS of northbound traffic all the way to Flagstaff. That portion of the trip will take much longer than you think. Load up with lots of bottled water for your journey while still in Phoenix, if you're a Costco member stop at the warehouse at the Yorkshire exit off I-17, on the north side of town. (Exit at Yorkshire, turn left and you will see the warehouse, E-Z off/on for the northbound driver.) Head for the rear left side of the store and pick up a case of Kirkland water bottles, you will definitely need them for a 3-day Arizona roadtrip in June.

The road is interstate to Flagstaff, easy driving but crowded on Friday nites. Once off the interstate you will be driving north on Hwy 89 out of Flagstaff. After you leave Flag you will need to be very alert for livestock on the road, especially once you cross the "border" onto the Navajo Nation (reservation). Observe the speed limit and stay very alert since it will be nighttime. I used to travel to this area every month, for about 5 years, on business. I would never drive on the reservation roads at nite, cattle can suddenly appear anytime. Stay at Cameron Trading Post, a gem of a place and a slice of the great American west.

A note on "time" during the summer. Arizona does not observe daylight saving, the Navajo Nation does, although some businesses near Flagstaff stay on Flagstaff time. Very confusing. Just use your own watch or alarm at Cameron, no telling what time the local clocks will say!

Get up Saturday and sure to eat breakfast in the tin-roofed old restaurant at the motel/trading post. Head west on Hwy 64 to the Grand Canyon. Spend the entire day at the Grand Canyon. Be sure to stop at Desert View. I'm not sure what the traffic & transportation system is at the Canyon at that time of year, you might have to park your car and take a shuttle bus. Be sure to walk all around the main overlooks near the El Tovar Hotel, try to have lunch there as it's a classic experience. Go to all the observation points that you can, each one presents a unique view of one of the world's seven wonders. Wear sunscreen, a hat, sunglasses, and drink that water!

You could stay at the Grand Canyon on Saturday nite, but it would be cheaper and probably more fun to head to Flagstaff, about a 90 minute drive. It's a fun town with a beautifully preserved old downtown area, a vibrant university scene, bars, restaurants, many hotels, B & Bs, and motels. It's the gateway to the Grand Canyon and the jumping off place for hikers, Colorado River rafters, etc.

Get up on Sunday and head down Oak Creek Canyon to Sedona, poke around the town, take a Pink Jeep or similar tour if you like, take a hike, look at galleries and shops, enjoy the busy tourist scene. Head back to Phoenix plenty early, the traffic will be extremely heavy all the way back and you should allow twice as long as you think it would take to get from Sedona back to Phoenix. Stay near the airport to avoid the Monday rush hour.

Your time on this trip is too short to do both the Grand Canyon and the Monument Valley plus Canyon de Chelly. Come back another time to do the great sights on the reservation. Enjoy Arizona!