To solve this question, the user needs to understand the meaning of the given sentence and the idiomatic expressions provided as answer choices.

The given sentence is asking the listener to wait patiently while the speaker makes a phone call.

Now, let's go through each option and eliminate the ones that do not fit the meaning of the sentence:

A. call the dogs off: This idiom means to stop pursuing or attacking someone or something. It does not fit the meaning of the given sentence, so it is incorrect.

B. have a whale of a time: This idiom means to have a great time or enjoy oneself. It does not fit the meaning of the given sentence, so it is incorrect.

C. flog a dead horse: This idiom means to continue to pursue a goal or idea that is no longer viable or useful. It does not fit the meaning of the given sentence, so it is incorrect.

D. hold your horses: This idiom means to be patient and wait. It fits the meaning of the given sentence, so it is the correct answer.

Therefore, the answer is: D. hold your horses.