When dividing most common English phrases into topics, it is wise to know how important it is to learn what a language function is. Namely, functions in English are phrases used to express a specific purpose. They are different from phrases based on a topic, because they are much more general, and can be used in any situation
Now, can you see that for each set of phrases based on a topic, one can use a number of appropriate functions in English?
For example, if you learn functions for interruption, and you can successfully use them in any situation.
It is also important to emphasize that when listing functions, it is always wise to list them in an order, according to the level of formality, so that a student can tell which functions are most appropriate in a specific context.
Now, how essential is it for a student to be able to tell the difference between functions and phrases ?
It's not important at all: if a teacher subtly introduces all these useful phrases and functions in English, students needn't know what they are called, but they should be taught to use them appropriately. If they do so, they'll feel much more confident when speaking English and such knowledge can only add up to their fluency.