1. Hi, this is Jane. 2. (formal) May I speak with John Smith? 3. (informal) Is John there? 4. I'm calling about... 5. I'm returning your call. 6. (formal) One moment, please. 7. (informal) Hang on a sec. 8. He's not here. Would you like to leave a message? 9. Could you ask him to call me back? 10. Thanks for calling.
The above steps do not imply that you should work yourself to the point of exhaustion. You need to protect your health and the integrity of your job. Working yourself to a frazzle constantly makes you prone to mistakes. When youre so tired that you realize its taking you twice or three times longer to do a job than normal, you need to call it a day. Rest at least a few hours and come back fresher, so that you can be strong at the end of the job. Learn how to power nap.