Update my phone with iOS 15.7.3

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

We need find out whether your iPhone is qualified for the new update.

What model iPhone do you have? Not sure?

Settings > General > About > Model Name

What version of iOS is now installed on the phone? Not sure?

Settings > General > About > iOS Version

I have an iPhone 12 and it will only allow me to install iOS 16. I don't want to do that, because iOS 16 is bloated and designed for newer, faster phones. I want the latest version of 15 because apple's own websites no longer function in the version of 15 I have. Is there a way to force my phone to get the latest version of 15 so I don't screw my phone up with 16?

Help me update my ios15.7.3

Is there a way to force my phone to get the latest version of 15

Apple does not support this.