From Overture Customer Email:

Phrase and Broad match types help you attract more customers by displaying your listings for a wider variety of relevant searches on Web sites. We are pleased to announce that Yahoo! now displays Phrase match type ads.

Weird how they talk about broad match there at the begining and then state that Yahoo! now shows phrase (and mention nothing about broad match ads on Yahoo!). Its a step in the right direction though if they are to extend out their ad delivery to more search queries.

Overture

• Exact Match: only shows up when the exact word / phrase is searched for.

• Phrase Match: shown on any search query that has that exact phrase in it.
• Broad Match: shown when the words are anywhere in the query (can even be separated). also shows for many similar type terms.