Using a proper dslr or mirrorless does make a measurable difference in terms of the depth of focus, aperture, image size, speed, etc. The lenses in the latest iphone can't really compete with a quality camera lens.
However as I mentioned those cameras are not fun to carry around all day unlike my phone. They are bulky and heavy, so I prefer not to use them except in important events or just around the house. And these days phone cameras are getting rather good for the average user's use case like posting to instagram.
Everyone says this until they see photos of the same event from a dedicated camera with a large optical path.