The phrase "be in to for" can be replaced with a number of different synonyms, depending on the context in which it is being used. Some common options include "interested in," "engaged with," "enthusiastic about," "passionate about," and "dedicated to." Each of these phrases conveys a slightly different nuance of the original meaning, ranging from casual interest to deep and committed involvement. Depending on the tone and context of the sentence, other synonyms like "fascinated by," "obsessed with," and "devoted to" might also be appropriate substitutions. Ultimately, the best synonym to use for "be in to for" will depend on the specific circumstances of the situation in which it appears.