Update my phone without wifi

You can't. Apple is serious when they state that you need to connect with Wi-Fi.

Possible workaround.......If your computer is connected to the network using Ethernet, you can connect the iPhone to the computer that way using the Finder on a Mac or iTunes on a PC.

Without Wi-Fi, your only option would be to upgrade your iPhone by connecting it to a Mac or PC that is connected to the network via an ethernet cable.

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Update your iPhone, iPad, or iPod touch with iTunes - Apple Support

38Carrielee Said:

"How can I update my phone without Wi-Fi"

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Updating an iPhone W/O Wi-Fi:

Use a Computer and Connect Using Ethernet:

Start with attempting an update through use of a computer. If you cannot use Wi-Fi, then use Ethernet.  Go Here: Update your iPhone Using a Computer - User Tip. On the computer, you would connect it through Ethernet, going directly into your router. For a Mac (or PC) that does not have Ethernet, this would be the adapter to use: Belkin USB-C to Gigabit Ethernet Adapter - Apple. If you get the same error, the model is likely just not compatible.

38Carrielee wrote:

How can I update my phone without Wi-Fi

You will either need to use a Wi-Fi Jetpack or MiFi device from your carrier (and not a hotspot!), a computer as mentioned above, or replace this iPhone with a newer model capable of 5G and with a 5G cellular plan,