Your biggest worries in Phoenix will be traffic & crime, lol. I take it you're making the 'Vegas Detour' to actually trash around in Vegas? Or to dodge ice on the skinny UT roads? If so, just know that Vegas has changed since the days of Obama.
I've run every inch of I-15 along that route, more times than I can remember... you'll want chains in your rig just in case some areas require 'em, otherwise you're good to go. Hopefully you get a good weather window for the run.
There are a couple of stretches in southern Utah which occasionally require chains IF the weather is nasty enough, so keep that in mind... but if you keep tabs on the weather, you should be able to run down into that high & low desert sunshine.
Don't forget the kick@$$ view of Hoover Dam from the *new* bridge, that's worth a gander. If you haven't actually done the 'Dam Tour' it's pretty cool, but I have no idea what the status is of touring, AYE? With the fraudulent Covid scene...
Anyway, you'll want extra gear & clothing aboard your rig, just in case ya run up on foul weather... I'd carry water and coolers full o' food as well, or else just some dry goods, but ya want SOMETHING, lol. Beef jerky always works, lol.
Moi, I'd have fartsacks & Arctic gear aboard that rig, but if ya time the run right, so you're hitting the high stretches in daylight hours, you should be alright. Know that there's just as much crime in Vegas as there is in Phoenix...
I wouldn't leave ANYTHING unattended in either location, it'd be likely to grow legs and walk away, lol... I had a reefer fuel cap stolen in Vegas one time, off the loaded trailer (IBP) I was dragging to San Diego, lol.
No big deal, I wrapped the neck in plastic kitchen wrap (multiple times) and used stout rubber bands to keep the plastic in place. Dressed it all up in silver duct tape to resemble a 'fuel cap' and made it past the coops in Kalifornia, lol...
Anyway, good luck on your run, plenty of trucks running on I-15, particularly on that stretch between the I-70 split in Utah clear on down to L.A. and San Diego, ugh. Good thing you're turning toward Henderson outta Vegas, lol. Cheers!