In this clip, Candace describes herself as being "heartless"; this is obviously meant figuratively, not literally.

In this clip, Candace has to answer a call and tells her mother she is "taking" it. This is an idiom; one does not "take" a call so much as they answer it.

In this clip, Dr. Doofenshmirtz tells Perry the Platypus to "have a taste" of his ray gun. He isn't proposing that Perry literally taste the gun; he is telling Perry to experience it.

In this clip, Phineas and Isabella sing about how they could have been "an item", which is another way of saying a couple.

In this clip, something is described as being "as old of time". Except for time and perhaps the universe itself, this is impossible.