Phantom Ranch and....
 

I am going to try to score a phantom ranch reservation tomorrow for next year at Christmas. we will likely fly down to the area and have approximately 9days in the area finishing with the hike to phantom ranch. Because we have kids we will stay a night on the rim, 2 at phantom ranch, and then 1 more night on the rim (or start the drive back to Vegas for flight the next day??) that leaves about 5 days at the start of the trip to see what we can! It will be December so daylight will be short and road conditions in some areas may be tough. any ideas/suggestions? Death Valley this time of year? anything else that really jumps out as amazing? Not interested at all in spending any time in big cities such as Vegas. Thanks in advance!! Planning a year in advance and I'm still overwhelmed :)

Guessing you will be flying into and out of Las Vegas.
Either on the way to the south rim or coming back, stay at the Hoover Dam Lodge which is about 3 miles from Hoover Dam.
Two things that are closer to LV are Valley of Fire and the Red Rocks.
It's not really worth it to go to Death Valley with the short time you have.

Red Rock Canyon and Valley of Fire are both easy day trip places but be sure to bring lunch, drinks, snacks as there isn't any place to get them in the parks.

I've done Death Valley as a day trip from Vegas several times because I find it awesome. It takes a bit over 2 hours to get to the valley. My favorite approach is to go north on 95 to the town of Beatty then head west. There is a well marked road on the right into the ghost town of Rhyolite which has ruins and one house made of bottles cemented into the walls instead of bricks.

The panoramic view from the top of the ridge is great. Stop at the pit toilets and cross the road.

For a quick trip, head down into the valley, go south and stop at Borax Works, Furnace Creek VC, through Artist Pallet Drive then down to Badwate then head back and see Zebrinski Point before heading back to Vegas through Parumph.

Fly into PHX, stop over for a few days in Sedona.

I'd also recommend spending more time in the southern half of Arizona rather than flying into LV. There's a lot to see and do there, and Sedona offers a nice red rock experience in a smaller setting. Even Phoenix, while a big city, offers nature very close by.

If you do decide to fly into Las Vegas, then I'd recommend either Zion in Utah or Death Valley. It really depends on your interests.

I hope you had luck in getting your Phantom Ranch reservation! If so, is it safe to assume you know about winter trail conditions at Grand Canyon, and the possible need for special equipment?

Your family must be strong hikers, given the GCNP schedule. In that case, my first recommendation would be to add Zion National Park. Zion may be a bit cold, but it will be warmer than GCNP. As long as the trails aren't icy, you have lots of great hikes. Observation Point is a top choice -- to my mind, even better than Angels Landing. I once hiked it in a minor late-season snow storm, and it was still worth it.

I also agree with others' mention of Death Valley. However, there's one caveat. If you plan on staying at Furnace Creek Ranch (the most common choice), their website has a notice: "Please be advised--due to construction, the restaurants, General Store, Registration Building, and the front entrance at Furnace Creek Ranch will be closed from April 17, 2017 to May, 2018. A temporary food service facility will serve quick service items. There will be a limited selection of retail items during this time. Construction noise should be expected between the hours of 9am to 6 pm daily. All dates subject to change."

Re: emalloy
I agree to start from Beatty.
IF you have a high clearance vehicle I strongly recommend driving Titus Canyon that is a 23 mile drive ending at DV valley.

It is a geological fantasy plus some an old 'salted' mining town.

Entry is just west of Rhyolite
Look at a DV map available from their web site.

emally recommended bottom two site - I agree.
Artist Pallet - be there 30+ minutes before sunset
Zebrinski Point - be there 30- minutes before sunrise

Vaga