* Phrases are fluid: The definition of a "phrase" is open to interpretation. Is it a fixed expression? A short sentence? A group of words with a specific meaning?
* Constant change: English is a dynamic language. New phrases are constantly being created and old ones fall out of use.
* No central authority: Unlike words, there's no official dictionary or body that keeps track of all phrases in the English language.
Estimates are wildly variable: Some estimates suggest millions of phrases, but there's no way to verify these.
Focus on understanding: Rather than trying to count phrases, it's more useful to focus on understanding how phrases work, their meaning, and how they are used in context.