I keep getting a pop-up that says: "iPhone Memory is Full"

keep getting a pop-up that says: "iPhone Memory is Full". It then prompts me to "Clean Memory" by clicking on a link which it claims will then direct me the App Store where I'm supposed to install the "Smart Cleaner" app. There is such an app in the store, but I'm still pretty sure this is some type of scam because when I check my phone's capacity, I have 83GB available from a total capacity of 128

[Re-titled by Moderator]