Present Active: Christine talks on the phone.
Present Passive: The phone is talked on by Christine.
Past Active: Christine talked on the phone.
Past Passive: The phone was talked on by Christine.
Present Active: Christine talks on the phone.
Present Passive: The phone is talked on by Christine.
Past Active: Christine talked on the phone.
Past Passive: The phone was talked on by Christine.
Sentences where the main verb is a form of “to be” (e.g., is, am, are, was, were, be, being, been, etc.) are neither active nor passive. The passive examples are ambiguous, because there’s no way to tell whether “is talked on” and “was talked on” are compound verbs, or whether “talked on” (really “talked-on”) is a participial adjective describing “phone”. (“participial adjective” means an adjective made out of a verb.)
Less ambiguous:
Present passive: “Christine is called on the phone by her friend.”
Past passive: “Christine was called on the phone by her friend.”