A Verb Phrase is a group of words which work together in the same way as a single verb does.
For example, the verbs in the sentences below are highlighted bold.
She slept soundly.
The dog barked all night.
In the following examples instead of a single word acting as a verb, we are using verb phrases.
She was sleeping soundly.
The dog was barking all night.
As you can see, a verb phrase consists of a main verb plus one (sometimes more) auxiliary verb, modal verb or participle.
had been sleeping
Some grammarians, use the term verb phrase differently. Depending on who you read, the following phrases in bold all count as verb phrases (even thought the first one is actually still only one word).
He had slept.
He managed to sleep through the night.
In this third example, the verb phrase is equivalent to the predicate.