Can't remember where we learned this or how it even started, but we have had great success keeping our wax worms in a plastic bin with about 1" of oatmeal. We find that we can make it through a bin of 500 or so with very few if any deaths. We do this with butter worms as well. But for what ever reason, it didn't work with Phoenix's worms. From what I understand there natural food is honeycombs, honey, bee pollen, bees wax. Also your not suppose to refrigerate them, if you keep them at around 65 degrees they don't grow as fast and will last longer, kept around 75-85 they will grow fairly fast in their cycle, but hey, what Cham doesn't like a good fat wax worm?
I keep my butters and wax worms in oatmeal or bran in the fridge. No need to feed them. Reptiworms need to be kept more moist in a topsoil substrate and not in fridge and I feed them all the old greens, fruits, sweet potatoes that the crickets or roaches don't eat. If the bran/oats get wet the butters and wax worms will die so keep an eye on the humidity and if it seems to be wet change out the bran/oats.
Once in a while. One or two every week or two. I don't use them at all. Silkworms, hornworns, superworms, phoenixworms. Check out nick barta for crazy stuff that is safe to feed. Will break the boring everyday cycle and be healthy.