A phrase is a group of words that doesn't have a subject and a tense verb.
A phrase cannot be a sentence. A phrase cannot be a finished thought on its own. Sentences can have many phrases. Phrases can have other phrases or clauses.
Examples:
closing the door
under the tree
because of his illness
on the shore
Other examples include expanded noun groups (noun phrases, nominal groups), prepositional phrases and verbal groups (compound verbs/ verbal phrases).
Expanded noun groups (also called Noun phrases/ nominal groups)
The high school girls basketball coach
The shiny, new red car
The grumpy, tired old cat
The car that I bought last week
The whole phrase (group of words) works together as a noun. We can replace "the shiny, new red car" with one word: "it". It has one main noun, called the "head noun".