When prepositions appear in the form of phrases (groups of words), they are called Phrasal Prepositions. It comprises, essentially, a simple preposition and some other word(s).
- In case of a fire, you should sound the fire alarm
- Out of ignorance, people break rules.
- You get $ 100 in lieu of an hour’s work.
- All that glitters is not gold according to a popular saying.
- By dint of an extraordinary performance, the student won a gold medal.
In the above examples, the highlighted groups of words (In case of, Out of, in lieu of, according to and By dint of) act as prepositions. Hence, these groups of words are phrasal prepositions.