Am trying to update my phone to the latest version

Since you have not told us the model iPhone you want to update, I can only guess. You have chosen the link about iOS 12.5.7 which leads me to believe that you have an older phone. Many older phones cannot update to the latest version because they lack components needed to run newer software. If you will tell us the model, we will be able to give you a better answer.

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.7

• If you have an iPhone 6S through 7, you can update to 15.7.5

• If you have an iPhone 8 or higher, you can update to 16.4.1

Go to Settings > General > Software Update.

This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support Update your iPhone or iPad - Apple Support

This link will show you how to update using your computer -

Update iOS on iPhone - Apple Support Update iOS on iPhone - Apple Support