If you don't fiddle with the phone camera photos much and are happy with them, there's not much difference. A $1k-ish mirrorless is a much more capable camera but it doesn't fit in your pocket and has about as many controls as a nuclear reactor control room.
Dedicated cameras have around 20 Megapixels but much larger sensor size - but does it really matter if the most I would do is print them into a photobook?