Why can't I update my iPhone?

What model phone, and what do you want to update it to? If it is a 14 Pro Max with iOS 17 it should update to 17.1.2 when you go to Settings/General/Software Update.

To update over the air from the phone all of these requirements must be met:

• You need at least 10 GB of free storage for iOS 17; more is better
• You must be connected to a Wi-Fi network (and not a personal hotspot) unless it is connected to a 5G cellular network
• The phone must be charged to at least 50%, and preferably plugged in so it stays above 50% during the update
• The phone must not be in Low Power Mode
• The phone must not be connected through VPN, and it may be necessary to delete any VPN apps and VPN profiles
• The phone cannot be in Airplane mode and must have a cellular data connection
• You cannot still have a beta of a previous version installed on the phone
• You cannot have a previous version that was downloaded, but not installed - go to Settings/General/iPhone Storage to look; if you find an iOS installer, delete it

If you can't meet all of them you can still update using your computer.