Unable to add phone numbers to current contacts in Outlook 2003

[vaders.bane]

I am using Outlook 2003 with Outlook Exchange Server. The exchange server is
syncing with a smartphone using ActiveSync. There are 3-5 contacts in my
contact list that I cannot add phone numbers to. I can change address,
e-mail and name, but not phone numbers. Does anybody know why this is
happening?

Thanks