How can I reset an iPhone with broken screen not connected to internet

From Erase iPhone - Apple Support (CA) :

When you delete data, it no longer appears in apps on iPhone, but it isn’t erased from iPhone storage. To permanently remove all of your content and settings from your iPhone, erase (wipe) your iPhone. For example, erase iPhone before you sell it, trade it in, or give it away.

[snip]

Use a computer to erase iPhone

You can use a Mac or Windows PC to erase all data and settings from your iPhone, restore iPhone to factory settings, and install the latest version of iOS.

1. 1. Connect your iPhone to your computer with a USB or USB-C cable. You may also need an adapter. See Connect iPhone and your computer with a cable.
   2. Turn on your iPhone.
   3. Do one of the following:

• • • On a Mac (macOS 10.15 or later): Click the Finder icon in the Dock to open a Finder window, click the iPhone button in the Finder sidebar (below Locations), click General at the top of the window, then click Restore iPhone.
    • On a Mac (macOS 10.14 or earlier) or a Windows PC: Make sure you have the latest version of iTunes (see the Apple Support article Update to the latest version of iTunes). Open iTunes, click the iPhone button near the top left of the iTunes window, click Summary, then click Restore iPhone.

I'm not sure, but you may have to tap something on the phone agreeing to "trust" the computer it's connected to, but I don't think you'd need to do any lengthy typing, at least not until you want to complete the setup with a new Apple I.D. etc. Perhaps the "trust" thing is only for syncing one that's already set up and running.

Is that what you had in mind?

[edit - It does not specifically say so, but you probably have to have the computer itself connected to the internet. I'm just guessing. Apple documentation is notoriously patchy that way.]

You're welcome.

Let us know if it works.

Or if it doesn't.