My wife and I did the trip you describe, we stayed one night, and we survived (well, sort of -- the day after we walked out we debated whether we needed to see a doctor). But, to me, the key words for you are "We're novice hikers."

Does this absolutely require that you spend two nights? No.
But will you be 100% certain that you WON'T need a second night? Unfortunately, the answer is also, 'No.'

For me, the problem is that you have you have no way of knowing the answer to the question of how long you'll need to stay -- and The Canyon is NOT a place to over-estimate your abilities!

Because you're novice hikers, you won't have a good handle on your hiking abilities. And, even if you find you're fully capable of walking the miles on back to back days, the simple fact is that desert canyon hiking is different from other kinds of hiking. Not necessarily more difficult, just different. And, unless and until you get a handle on your talent in this challenge, I'd recommend you not risk a problem by giving yourself an extra day to recover.

In many other places, you can decide that very day that you need an extra day of rest. This will NOT be possible at The Canyon, as the Rangers will tell you to either start walking or pay for a helicopter evacuation, which will be done ONLY for a medical emergency. Too tired because of bad planning on your part? -- that's YOUR problem!

If you take my advice to stay a second night and you don't need to do so, I hope you won't curse me. But if you don't take my advice and it turns out you do need to do so, you'll definitely be cursing yourself!

You can always use the 2nd night to do a bit of exploring while your down at the bottom.

If you can go two days, then heck yeah do it.

I have yet to hike to Phantom, but it is high high on my list.
I hope to go rim to rim when I do attempt it.

In talking with a friend of mine, who hiked it in May, she thinks that October would be the very best month.

I would suggest finding some hikes and do a few that have some serious elevation gain/loss to condition youself.

I guess you know that you will want to try at the very moment that reservations become available(I would even try on multiple phones with multiple people).

I stayed one night but probably could have used two. If you have ANY problems with knees, ankles, feet etc, even a slight problem is going to be greatly aggravated.

A great website that really helped me prepare in a lot of ways is www.hitthetrail.com
They suggested gel toe pads like ballerinas wear. I loved mine--no problems with my toes at all.

When you call for reservations, be prepared to make your rim reservations the night before and the day you come out. Also, be ready to tell them which meals you want at Phantom. I highly suggest you order the packed lunch for the day you hike out. It was full of foods that will give you the energy you need.

When you make that phone call, you will be making all these reservations at once. You may be making the call in a very early hour in the morning on the date your reservation opens. It helped me to have it all written out.

2 nights for sure, 3 would be even better.

If you're gonna make the effort to get down there, why wouldn't you want to linger and explore? It's way too cool of a place to just spend one night. I only had 2 nights there and 1 at Indian Gardens - if I did it again I would definitely skip Indian Gardens and add the extra night to Phantom.

I went in early November and weather was great. October is fairly popular.