Why can’t I update my phone

It all depends on the Model Name of the iPhone.

If you check Settings > General > About.......what is the Model Name of your phone?

If it is iPhone SE 1st Generation.......the phone cannot be updated to iOS 16 or iOS 17, if that might be what you are asking about.

What type of iPhone is it? iPhone 8 and lower don’t get updates. Xs and higher get updates. In the description it says iPhone SE 1. That is based on iPhone 6s which isn’t supported anymore.

it might be because your phone doesn’t support an update anymore