Am I Able To Add A Phone Number Or Email To the Header of My Storefront?

The phone number you have on the storefront be default is the only way you can add a phone number to the Header using the tools in the Admin.

The phone number position changes depending on the Theme Setting you are using.

You would have to use some custom coding using CSS, HTML or JS in order to add an email or a phone number to the Header to be different from the Admin tools provided.

Here are a couple of recommendations for you can do if you do not have access to Custom CSS, HTML, or JS coding:

1) You can create a Header in Photoshop that would include your logo, phone number, email, or whatever else you want. This header would basically be replacing the logo that you upload.

You would have to play with it for the length and width of course.

2) You can create a Banner/Slider with your phone number on it. that is right below the header.