I'm aware of what phrasal verbs and the fact they are typically accompanied by a word like up, down, or in in order to add meaning to the verb. But, in the sentence: The subject is whom or what the sentence is about, is 'is about' a phrasal verb? I know the object pronoun whom here should be the object of the preposition about, but isn't the word 'about' here linked to the verb 'is'? If so, then shouldn't whom be changed to who? If so, are there any other examples of linking phrasal verbs?
I may be completely wrong on this, I am just a bit perplexed and curious to know. Thanks!