How to make iMessage on my Macbook Pro merge with my iPhone's phone number like it used to?

How do I make iMessage on my Macbook Pro merge with my iPhone's phone number like it used to?

Added (1). When the Messages app first popped up on my Macbook, I could send and receive texts from my phone number while typing from my laptop. Now, it sends and receives from my iCloud account name and I'm having two separate conversations with the same person! I would like the texts I send from Messages to come from my phone number, not my iCloud email.

You forgot to tell what you have. My answer is for OS 10.10 or later, and iOS 8.1. No other systems will work with Mac Messages SMS.

In Messages, top menu bar, click the Messages menu > Preferences, remove the checkmark for the email.