It's completely normal. Has been since the very first lens was made. Lenses are curved, so unwanted refraction is always going to be something to contend with.
An iPhone is not a professional camera. Sorry, but it just isn't. Nor is the camera in any other cell phone. Not that the pro iPhones don't take nice photos and videos, considering there's only about $200 worth of parts that make up the camera. My iPhone 14 Pro takes nice shots, but I would never call it a pro camera. There are a lot of limitations to a camera that has a 24mm lens as its least distorted optics.
My Nikon D800 was $3,400 new. And that was just for the body. A 1.4 50mm lens was another $350. $1,250 for a 24-300 zoom. And no surprise at all to me, I would get lens flare depending on the angle of my shot relative to the light source. And even the D800 was at best a prosumer camera compared to a PhaseOne, where the lenses alone cost more than the D800 body.
Is there more lens flare with the iPhone 17 Pro? Probably, but it's also entirely understandable when you consider the optics. There is a true optical zoom up to 200mm. That means more lens elements and more groups in order to achieve that. More lenses means more refraction. More refraction means more possibility of flare.