Learn Polish: Dyrektor będzie jutro z tobą rozmawiać. - The director will talk with you tomorrow.

The preposition z meaning "with" always requires the noun or pronoun that follows it to take the Instrumental case. Tobą is the Instrumental form of the basic pronoun ty (you).

Why are we using "będzie" and "rozmawiać" together?

This is how you form the future tense for many verbs in Polish. You take the future form of the verb "to be" (here, będzie meaning "he/she will") and add the infinitive, or dictionary form, of your main verb (rozmawiać).

Why are "będzie" and "rozmawiać" separated by other words?

Polish word order is very flexible! It is perfectly normal to place time words like jutro (tomorrow) and phrases like z tobą (with you) right in the middle of a two-part verb. You could also say Dyrektor będzie rozmawiać z tobą jutro, but the sentence's current order sounds very natural.

Could I use "mówić" instead of "rozmawiać" here?

It would change the meaning slightly. Rozmawiać means "to talk" in the sense of having a two-way conversation, which is why it pairs perfectly with z tobą. Mówić means "to speak" or "to say" and focuses more on the person producing the words rather than the back-and-forth exchange.