Clauses are like full 'sentences' (but not in the sense of punctuation) because they have a subject and a verb/predicate. But clauses can be embedded in one another (that's how they differ from sentences, which are stand-alone by definition).
Phrases are any group of words, such as "the book", so they don't necessarily involve a subject or a verb/predicate.
All sentences are clauses.
All clauses are phrases.
All words could technically be considered phrases (although sometimes the term implies "multi-word phrases").
There are many phrases per clause, because they are embedded within each other.
