INFJ's Fi is unconscious and is responsible for part of the INFJ's ulterior worldview in the Ni-Fi mechanism. There is false identification with the Fi function (as in relating to it as a conscious function) due to its unconscious presence in the INFJ's thoughts and decisions.
In Socionics, the INFp's Fi is the Demonstrative Function, which is essentially the same information as the written above, with some added inter-type relation features. For instance, the Demonstrative Function of a type is that type's dual's PoLR, meaning that if an INFp's dual's (ESTp) Fi PoLR gets hit unfairly by any Fi Ego valuing type, then the INFp will usually respond by slamming the Fi Ego type with Fi Demonstrative, which is released negatively usually against threats and much more powerfully (due to the fact that it is A. An unconscious function, and B. treated as though it is useless when used consciously). The Beebe model in JCF describes the Senex/Witch function as an assertion of authority to counter another's use of Fi against the common goals of the IxFJ.
Also, once-a-fucking-gain, the INFJ's most common types are Type 4, Type 5, and even Type 2 before Type 1 and cannot be specifically correlated directly with any type due to the nature of the Enneagram system, which works on motivations, fears, and drives rather than how the psyche functions. Sure, it can be extrapolated what certain JCF types want from functions such as the inferior, but these desires due not usually translate into Enneagram motivations or drives.