Bugs?

I noticed that when you create a new contact you have a field called "main phone". Next time you open this contact after saving the field "main phone" is not visible on the contact. Only office phone and mobile phone is visible. When you create new activities, for example a phone call to this contact it automatically picks up the number you entered in "main  phone" when the contact was created. How do you change the "main phone" number.. surely netsuite doesnt expect that phone numbers stay the same forever? If somebody has some good tips it would be appreciated.