Clause, phrase and sentence:-

The basic unit of English grammar is the clause:

[An unlucky student almost lost a 17th century violin worth almost £200,000] 

[when he left it in the waiting room of a London station.]

[William Brown inherited the 1698 Stradivarius violin from his mother]

[and had just had it valued by a London dealer at £180,000.]

Clauses are made up of phrases:

[An unlucky student] + [almost lost] + [a 17th century violin worth almost £200,000] 

[when] + [he] + [left] + [it] + [in the waiting room of a London station.]

[William Brown] + [inherited] + [the 1698 Stradivarius violin] + [from his mother]

[and] [had just had it valued] + [by a London dealer] + [at £180,000.]

We can join two or more clauses together to make sentences.

An unlucky student almost lost a 17th century violin worth almost £200,000 when he left it in the waiting room of a London station.

William Brown inherited the 1698 Stradivarius violin from his mother and had just had it valued by a London dealer at £180,000.