Your resume is the first impression that potential employers will have to determine if you're the right for their company. You will want your resume to have perfect grammar and punctuation, including the proper formatting of phone numbers and extensions. Listing phone numbers can vary from country to country. Be sure to make your contact information easy to find, preferably listing it in bold toward the top of your resume.
Adding a Phone Number
Write the phone number with your contact information. You should include the area code as well as the phone number. It should look like (555) 555-5555 or 555-555-5555, depending on your preference.
Adding an Extension
Write out "extension" with the extension number beside it or simply write "ext." with the extension number beside it on the same line as the phone number you are listing. It should look like either (555) 555-5555 extension 5 or (555) 555-5555 ext. 5.