How to Change the Default Fields for iPhone Contacts
Your iPhone contacts' profiles provide a way to keep track of a variety of information about your friends. Aside from attaching a first and last name to a specific phone number, the Contacts application can also store birthdays, middle names and other details. By default, your iPhone asks you to fill out a few bits of information, including phone number and email. Additional fields can easily be added and the information currently in a default field can also be edited.
Tap on the "Contacts" icon on your iPhone's Home screen.
Tap on the name of a contact to open her profile, and then select the "Edit" icon in the top right corner of the screen.
Change the information in one of the current default fields by tapping inside the field once and using the keyboard provided to enter new information. Use the backspace to delete current information first, if applicable.
Scroll down to the bottom of the contact's profile fields and tap "Add Field." Select the field you want to add to the contact, such as "Nickname" or "Job Title." Enter information into the new field when prompted.
Tap the blue "Done" icon when you have finished making changes to the fields.