Yes, I could see this being a cause, but not in my case, as I clean the lenses before making the snaps. The trouble is, there's not a way for me to be sure whether or not the 'less crisp' impression is real, or just in my imagination.
I suppose that the only route open to me is to run a series of tests, but that's not going to happen because I know I'd find it too boring half-way through any testing. And of course, the tests themselves wouldn't be conclusive because there'd be no way to make them using the cellphone as a new unit again, to provide the 'new' comparitor (nice neologism to fill a gap that shouldn't exist!).
Perhaps this is all a September affliction, brought on by new iPhone release expectations brought to their peak each year at this time. So far, the only big expectation that seems likely to be certain is a hike in prices. Telefonica has already been offering deals on the existing iPhone 17, but intentionally buying old doesn't strike me as making much sense, as it's the photo side of the new 'phone that has been getting all the pre-release hype and photography is the only reason I'd be interested in a new cellphone.
There are also rumours of new cameras on the way, and if Nikon comes out with something really small, much smaller and lighter than my old D200, perhaps that might make more sense because I have a stack of good lenses doing nothing... sadly, I suppose that a smaller camera would mean an even smaller viewfinder; the D200 - and also the dead D700 - both have accessory magnifier lenses fitted to the viewfinders, and those made a world of difference with both bodies. The Nikon Z 50 II seems to fill some of those requirements, but afaik has neither a sensor shaker to remove dust, nor even any form of stabilization. The price is right, as it comes below the current iPhone 17 Pro.