How do I get a birthday to repeat yearly on the calendar in my iPhone 14?

If you are creating a birthday event in iOS calendar simply select the Repeat field and choose 'Every Year'.

If you have your contact's birthdays recorded in the Contacts app you can add a birthday calendar to your iOS calendar app. This will draw the information from your Contacts app and repeat it on each yearly occurrence of the date. To do this open Calendar, touch on Calendars at the foot of the screen (in day or week view), then scroll to the bottom and select the Birthdays calendar.