I am TOTALLY with you on not arriving "day of". It's too big a risk, and too much stress at the beginning of what's supposed to be a vacation. Flights can go wrong at any time, even if it's just delays, and more so the last couple of years. Why do that to yourself unless you have to? You are definitely not alone in this; I think you'll find most of the folks on this Forum would agree with you.
At least in the past (and I can't imagine this has changed, but who knows) this is one of the few ABDs that does a "mass transfer" from the Airport to where the ABD starts in Sedona, so you likely will NOT be able to get ABD to pick you up on any day that's not the day of the start of the ABD. But since you are staying at the same hotel that the ABD starts at, it couldn't hurt to check (their policy on this changes all the time). However, if ABD isn't offering pre-nights, it's probably because of the mass transfer.
The motorcoach used to stop at Montezuma's Castle on the way to Sedona. I'm sad to see that doesn't appear to be the case anymore. But honestly, if they are still doing the mass transfer to the Enchantment, my suggestion would be to spend that first day and night in Phoenix, then meet the group at the Phoenix airport for the pickup and take the motorcoach to Sedona with everyone else. That's what I did, and it worked really well. There's bound to be some fun stuff and bonding going on during that drive (and possibly unscheduled stops) and it would be a shame to miss it. There's a TON of places to stay in Phoenix, plenty of stuff to do, and you'll be right where you need to be to be picked up day of. Just verify this all with ABD before you make any changes.
Again, this is assuming the pickup is the mass motorcoach transfer they've done in the past. Your TA can find this out from ABD. If it isn't, and they are doing individual pickups, then there's probably no downside to staying at the Enchantment the night before.
This is still one of my very favorite ABDs!
Sayhello