Classification of phrases

the sentence, is a basic unit of syntax, there is no universally accepted definition of the phrase.
All definitions of phrases fall into two groups: the modern approach and the traditional approach

at least two words, one of which is a notional word but which is not a form of a word.
   e.g. will have been writing is not a phrase but a form of the verb to write.
Do it is a phrase.

of at least two words belonging to the notional parts of speech. According to this approach the combination of words in the park is not a phrase because "in" is not a notional word.

kernel element is that on which the other one is dependent. If there is the kernel element in a phrase, the phrase belongs to the kernel group of phrases (a nice place, well-known artists, absolutely positive, to run fast, to see a movie, to taste good). 
If there is no main constituent in a phrase, it belongs to the non-kernel subgroup. The procedure which helps to see whether there is a dependent constituent or not is to see on the sentence level the possibility of dropping one of the constituents without destroying the identity of the sentence.

that part of speech, phrases are divided into 4 groups:

- noun-phrases:
A+N: a young man 
N+N: a brick wall 
N's+N: the girl's smile;
adv+N: the then government 
N+prep+N: a leg of the table
- verb-phrases:
V+N: take a shower 
V+adv: to walk fast 
V+adj: to look beautiful;
V+prep+N: to depend on the weather
V+V: to try to do
- adjective-phrases:
adv+adj: very interesting 
adj+prep+N: independent of the weather
- adverb-phrases: adv+adv -  very quickly