A long time ago, in a galaxy far, far away (Chicago, if you must know) my manager at the time told me that when I left a phone message I should always repeat my phone number twice, and slowly, at the end of the message. That was good advice.
I cannot tell you, because I have not counted precisely, how many times I have received messages at the end of which the caller rushes through their phone number as though it were information of little value, a mere punctuation to the call.
Even in such a people-oriented industry as staffing, I still occasionally receive such messages and they can take a little detective work to return. Of course, I make that effort to figure out the caller's phone number; but would a sales prospect or a high-skilled worker you are trying to recruit necessarily do so? Sometimes yes, sometimes no.
Your phone number is the most important information you leave, so repeat it slowly. Your phone number is the most important information you leave, so repeat it slowly.
Helps to have that key information repeated, eh?