We are calling to 'confirm your appointment' with Dr. Jones. = We are calling to make sure that you will 'keep your appointment' with Dr. Jones.
The museum is open to visitors 'by appointment' only. [=you have to make an appointment to visit the museum]
The court ordered the 'appointment' of an attorney to represent the child.
(..) I've caught you at last. This is Dr. Greene. Dr. Greene, uh, I'm sorry I haven't called you back. That's okay, but you've missed your last two appointments. Can you come to my office this afternoon? I did leave a lot of messages. I know. I-I've been so busy, (..)2018 Fifty Shades Freed