Answer:
les
Explanation:
Les is the indirect object pronoun standing for the third person plural. An Indirect Object Pronoun is a person that, in indirect way, takes the action of a verb and tells us to whom or for whom an action is done. We can see the different forms of indirect objects in Spanish in the Table below. In this exercise the action is being performed for Ana y Elisa, that is, for them, that's why we choose les instead of other indirect object pronoun. Finally:
Yo les hablo a Ana y Elisa por teléfono todos los días.