Some basic verbs in English easily link up with certain prepositions. These combinations give new and completely different meanings. Examples of basic verbs are get, make, set, do, come, put, go, look. Combined with prepositions they change meaning, e.g.: look for, look after, look up, or:get on, get by, get off.
The term "phrasal" refers to the fact that these verb+preposition combinations make a phrase (i.e. a meaningful connotation or expression).
These expressions are widely used in spoken English. There usually is a more formal alternative in written English that will express the same meaning. E.g.: To put in an application (to submit), to set up a new business (to establish).