Aw: Counting the number of repeated phrases in a column

> There is a short of a function in the standard Postgres to do the following:
>  
> it is easy to count the number of occurrence of words, but it is rather difficult to count the number of occurrence of phrases.
>  
> For instance:
>  
> A cell of value:  'Hello World' means 1 occurrence a phrase.
>  
> A cell of value: 'Hello World World Hello' means no occurrence of any repeated phrase.
>  
> But, A cell of value: 'Hello World World Hello Hello World' means 2 occurrences of 'Hello World'.
>  
> 'The City of London, London' also has no occurrences of any repeated phrase.
>  
> Anyone has got such a function to check out the number of occurrence of any repeated phrases?

For that to become answerable you may want to define what to
do when facing ambiguity.

Best,
Karsten