A sentence is a group of words containing a finite verb.
A phrase is a group of words that does not contain a finite verb.
A phrase is a unit of thought.
Like single words, phrases function as parts of speech and parts of the sentence.
Phrases may be as short as two words, or they may be much longer. The words in a phrase occur in a certain order. Changing the order of the words in a phrase would result in nonsense.
Here are examples of phrases:
after dinner
on the beach
coming around the corner
to be or not to be
have been missing
a small brown hamster
the car of my dreams
Before you try to understand phrases, MASTER THE PARTS OF SPEECH.