Phrasal verbs are constructions consisting of a verb and either a preposition, a particle, or both.
1. Prepositional Phrasal Verb
This construction consists of a verb and a preposition, as in “I take after him,” “We’re looking into that,” and “Please stand by.”
2. Particle Phrasal Verb
This construction consists of a verb and a particle, as in “She didn’t want to give in,” “I decided to follow up,” and “He left out the best part.” A particle phrasal verb can also be interrupted by a noun or a pronoun, as in “He tried to look the name up,” “I handed the assignment in yesterday,” and “We worked the details out.”
In these latter types of constructions, the particle can be relocated to be adjacent to the verb, as in “He tried to look up the name,” “I handed in the assignment yesterday,” and “We worked out the details.” Which alternative looks or sounds more natural varies randomly; in the first example, “look up the name” suggests viewing the name from a certain direction, while “look the name up” implies research, but the other two sentences seem better written when the verb and the particle are adjacent.
3. Prepositional-Particle Phrasal Verb
This construction consists of a verb, a particle, and a preposition. Examples include “I’m looking forward to a vacation,” She sat in for me during my absence,” and “They’re not willing to put up with it anymore.”
Note that many words serve as both prepositions and particles. As noted above, the phrase “look up” can refer to the act of directing one’s attention upward, but it also has a figurative meaning: When one looks something up — or, to be more formal, conducts research — sight, but not an upward motion of the head, is involved.
Take care not to confuse phrasal verbs and compound nouns (sometimes used as adjectives) that consist of the same words. For example, one signs up for a class but attends a signup session, or simply a signup.
Also, the prepositional phrases “in to” and “on to” are combined into one word only in certain circumstances: Into is correct when the reference is to a location, as in “I went into the doctor’s office,” a literal reference, as opposed to “I went in to see the doctor,” which is figurative. Onto is correct when you could precede it with up, as in “I climbed (up) onto the rock,” but in sentences such as “I want to hold on to this book,” the two-word form is preferred.
Notice, too, that phrasal verbs are generally colloquial and are seldom suited for formal writing; a more succinct alternative is frequently available. And even in informal prose, writers should consider omitting extraneous adverbial particles when a verb alone would do, as in “help out” in place of help.