why can I not update my iPhone 11 to 15.1.1?

It was on the update page in Software Update on the iPhone, as well as saying that it was to deal with call handling. However, you would not have seen that since you do not have the iPhone 12 or 13. Where did you look at the information about the iOS update?

iOS 15.1.1 was released only for iPhone 12 and iPhone 13 models. The issues it addresses are not present in iPhone 11.

captkidd0 wrote:

it would have been helpful if that had been stated in the update.

It is so stated.

Apple security updates - Apple Support

what happens when you try?