How do i authorize my Mac book air to my iTunes account on my phone

Authorization

iTunes Store- Authorize or deauthorize your Mac or PC.

In iTunes you use the Authorize This Computer or De-authorize This Computer option under the Store menu in iTunes' menubar. For Windows use the ALT-S keys to access it. Or turn on Windows 7 and 8 iTunes menus: iTunes- Turning on iTunes menus in Windows 8 and 7.

Change what? If you have authorized the computer you need not do it again. You don't authorize an iPhone, you only authorize the computer used with the iPhone.

Computer.

Authorization applies ONLY to computers.

As Kappy said, iphones are not authorized at all.

Using iTunes on the computer. See the link I posted in my first reply.

The menubar is at the top of the screen.