Hey _harryb,
Some models of iPhone, like the iPhone 13 Pro, iPhone 13 Pro Max, iPhone 14 Pro and iPhone 14 Pro Max have a camera dedicated to taking those ultra close up images that you'd generally see with what's called macro photography. This is a type of photography that is used when taking photos very close up. Is this the situation you're in? Also, is this happening in a dimly lit area, a well lit area, or both?
Take great photos and videos has some good tips on how to get the most out of the camera on your device. This includes tips on taking selfies, shooting photos and videos in low light , editing and more. That would be a great place to start with, along with testing the camera's behavior in varied environments and conditions to see if this blurriness occurs in every situation or only spcific situations.
Be sure to post back what you find out.
Take care.