Since most phones run at the same resolution as a desktop
... WTF is the purpose of a badly written mobile site?
Even if your phone's resolution matches your desktop resolution, the display is much smaller. Text that would normally be viewable on a desktop is infinitesimally small on your phone. Sure, you can zoom it, but then you're changing the way the website works because you are viewing just a small part of the page through a magnifier.
The real issue here is accessibility options for impaired users. Even mobile sites need to have text large enough for you to see....