Well, some phrases (and yes, phrasal verbs) get concatenated over time, like "understand", "overtake", "courtmarshal", "becalm", "whipsaw", etc. The conjugation

Well, some phrases (and yes, phrasal verbs) get concatenated over time, like "understand", "overtake", "courtmarshal", "becalm", "whipsaw", etc. The conjugation and number rules work themselves out eventually, for example, "courts-marshal", "overtook". It's just one of the ways languages mutate. Usually the noun form mutates first, and later on the verb form, but not always.