Organizing and accessing contact information in Outlook.com
Hi , first open Contacts >> Lists on your iPhone. Are your contacts under iCloud or Outlook? If they’re in iCloud, they’ll need importing into Outlook first—Outlook’s Save Contacts option only copies contacts to your phone.
Once they’re in Outlook, use the same account on your PC and iPhone Outlook app.
For birthdays, open Outlook.com on your PC >> Calendar >> Add calendar >> Birthdays and enable it. This uses birthdays saved in your Outlook contacts.