Although I trust LHs own stuff and info completely you should remember that they don't have any more insight in other producer's materials than the public gets. Since there aren't any regulations to the materials of sex toys or the info companies give you about them you never really know how safe they are.
The demand for phtalate free toys is high and companies say their toys are phtalate free even when they're not, apart from that there are other chemichals used instead of phtalates that can still degrade toys stored close to eachother.
As mentioned medical grade silicone can safely be stored together without risking them melthing together but any other plastics should be stored in bags (jelly, rubber, "skin safe" rubber, skin like feel things etc, you get it, this includes any "silicone" toys from less reliable companies). Even if certain combinations might be ok there's just no way of being certain what's what and it's a shame to come hope horny and find your favourite penis in a plastic puddle.