How can I connect my iPhone to iOS

Your post makes no sense. iOS is the operating system on your phone.

If you're asking to update -

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, or SE 1st generation, you can update to 15.7.9

• If you have an iPhone 8 or higher, or SE 2nd or 3rd generation,you can update to 16.6.1

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

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

Update iOS on iPhone - Apple Support

Your question does not make sense. iOS is the operating system that the iPhone runs on.

If you're trying to ask how to upgrade iOS, go to Settings>General>Software Update.