Using a new methodology, the paper reports experimental work that sheds light on the organization of the lexicon, the storage technique of phrasal idioms, and the derivation of various diatheses. We conducted an experiment to examine the pattern of distribution of phrasal idioms across several diatheses. Native speakers of Hebrew were taught invented Hebrew idioms inspired by French idioms. The idioms were headed by predicates of three diatheses: a verbal passive, an adjectival passive, and an unaccusative verb. After learning the idioms, the participants evaluated for each idiom how likely it was that it shared its idiomatic meaning with its transitive version. The results show that the distribution of phrasal idioms depends on the diathesis of their head. Subjects perceived the likelihood of the verbal passive to share idiomatic meanings with its transitive counterpart as significantly higher than that of both the adjectival passive and the unaccusative. The findings provide support for the claim that phrasal idioms are stored in the lexicon, not in an extra-grammatical component, since their perception by speakers turned out to be dependent on a grammatical property, the diathesis. This dependency can be explained if phrasal idioms are stored as subentries of their head. The findings also reinforce the view that adjectival passives and unaccusatives are listed in the lexicon, but not verbal passives. Finally, they support the existence of an active lexicon, where thematic operations can apply.