Please recommend a free iPhone Cleaning app

My best advice is not an app. It is to check the storage on your iPhone then follow the advice here:

How to check the storage on your iPhone and iPad - Apple Support

Best app by far is none.

OmahaRod wrote:

Please recommend a free iPhone Cleaning app

Apple devices, including iPhones, are “self-cleaning”, just like your oven. There is no 3rd party software that can do a better job than iOS itself, and most of the so-called cleaners and antiviruses do nothing useful a and just slow down your phone.

+1