Resampling to reduce photo size?

If I transfer a cell phone photo to the PC for Photoshop Elements, it has an initial resolution of 72 ppi and it's huge, something like 55 x 40 inches.  If I reduce this to let's say 10 x 8, the resolution remains 72 with resampling on. If resampling is off, it becomes 300+. What is going with the software to reduce the size of a photo with no change in resolution?  How can it physically reduce the size of the photo and not change resolution? That would seem to really degrade the photo too, at least technically (not sure I see it).  Why ever resample to reduce size?  Should resample always be off for reducing size? Thanks for any help explaining this.