The crucial bit is "things that need to be done or are desirable". Neither does the phrase "to file suit" need to be made a phrasal verb, nor is it desirable for it to become one. It either is one or it is not. The subjunctive has a function similar to the Russian particle бы. Imagine you would say (translation is hopeless here, but I guess you get the idea): "to file suit" было бы "phrasal verb". I think that doesn't make much sense, does it?
If you use subjunctive, then you say something to the effect "I wish that from now on "to file suit" (should) be considered as a phrasal verb". That's quite different from a simple "it is a phrasal verb".