If it's a phrasal verb, treat is as a single unit:
He was always (going off) (about things).
If it's a prepositional phrase, keep the preposition with the prepositional phrase:
She (will get) (off the bus).
She (will depart) (from the airport).
She will (get off) without spending any time in jail.
get off informal escape a punishment; be acquitted : she got off lightly | you'll get off with a warning.
Incidentally, one clue to recognizing when a word is part of a phrasal verb is when it is followed by a preposition. Take a look:
He was always going off about things.
She will get off with a warning.
Those consecutive preopositions show how the sentences should be parsed:
He was always (going off) about things.
She will (get off) with a warning.
However, this doesn't tell the full story; sometimes a phrasal verb is followed by an object, not a prepositional phrase:
Joe's barbs were really (getting to) Sally.
Here, barb means (from NOAD):
barb [figurative] a deliberately hurtful remark : his barb hurt more than she cared to admit.
while get to is a phrasal verb:
get to [informal] annoy or upset (someone) by persistent action
However, if we were talking about parcel post, we could also say:
Joe's packages were really getting (to Sally).
In that case, getting to is not a phrasal verb; the sentence simply means Sally was receiving the packages that Joe mailed to her.
However, if Joe was a would-be suitor, but Sally had no interest in Joe, we might say:
Joe's packages were really (getting to) Sally.
which would mean Sally was getting annoyed from too much unwanted attention.
So, the only way to know for sure is to (a) recognize the phrasal verb, and (b) know the context enough to understand the meaning of the sentence.