||Ah - I see. Well this is where it comes down to intent. Is the intent of the class simply to adapt the methods of the IRule interface to those defined in the PhoneValidator? If the answer is yes, then it would absoluetly be an adapter pattern.
However, the more the PhoneRule does outside of that context, the less it becomes like an adapter and the more like another strategy implementation of IRule. Example: if PhoneRule not only validates using PhoneValidator but also provides services like, Phone lookups (or some other phone related service) - then I'd say it's more like a complex object, that happens to use PhoneValidator to fulfill part of it's purpose, than it is an adapter...
See the difference (ie it's based on the intent)?