What time of year? Makes a difference with a few of the possible routes.
1) Temecula Wineries - 90 minutes or so from San Diego.
2) Drive Pine to Palm Scenic highway from Temecula to Palm Springs to stay a night.
In Palm Springs area do arial tram, see downtown Palm Springs, the Living Desert, have a date shake.
4. Drive from Palm Springs through Joshua Tree National Park, see the park, exiting to 29 Palms.
5. Drive and spend a night at Lake Havasu City taking a sunset cruise on the lake (if they are running).
Stay at London Bridge Resort
Things to see around Flagstaff include some interesting Native American rurins such as Wupatki and Walnut Canyon. There is also Sunset crater.
There is enough to see in Sedona to spend 2 or more nights
8. Then drive to Grand Canyon National Park as you have planned.
There is a good animal rescue drive through park in Williams called Bearizonia
9 Then complete your drive to Grand Canyon National Park.
Note: On your comment regarding Phoenix, there is a lot to do there, such as Old Scottsdale, Musical Instruments Museum, Heard Museum, zoo, Desert Belle boat ride in the desert, Lost Dutchman State Park, brew pubs in Tempe, and so forth. But you don't need to go there if you do not want to
As such, the suggested itinerary I have given does not include Phoenix.
It also does not include Las Vegas which is another place people like to include on a trip to Grand Canyon.
Desert parks east of Las Vegas such as valley of fire, zion, bryce are possible but can be subject to some winter conditions. Grand Canyon can have dusting of snow too dependent when you are traveling.
Awesome suggestions! Thank you