From what I read Phoenix worms are very nutritious, super high in Cali. But I have also heard of chams going on hunger strikes because they have been spoiled with worms so while they are healthy not too too many. But giving them a large variety of food is important so focusing on one worm isn't good no matter how nutritious. This chart shows some comparisons of other common feeders to Phoenix worms.
Notice they dont have butterworms on the list, the real high calcium worm
PS: phoenix/repti/what ever worms are just black soldier flies. They are only high in calcium due to their diet. If you raise your own or keep them out of the fridge and feed them something else, they are about the same nutrition as crickets etc.
If you want high calcium stuff i would try for some butter worms or silk worms if you have a mulberry tree near by.
I usually feed my Cham crickets, but my nearest pets shop is 3 towns away so I get about 70 crickets but he goes through them quickly. I try to give him mealworms as treats, he will eat some carrots, and he loves Phoenix worms. My pet shop doesn't carry butter worms or hornworms etc. but maybe grass hoppers? He will eat dead crickets (I can't put a live cricket on my nose... Yuck) when I train him when I Handle him so I can give him dead grasshoppers too.