I almost always have my phone, whereas I am not carrying (lugging) my dslr or even my mirrorless around. No thanks.
Unless you are printing these photos, the iphone's cameras are more than adequate for posting online.
Everyone says this until they see photos of the same event from a dedicated camera with a large optical path.
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.