Can I back up my iPhone before I restore it?

If your iPhone is running iOS 15.2 or higher........you can use the instructions linked just below:

How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support

If your iPhone is not running iOS 15.2 or higher........please use the instructions linked below, but note that you must use a PC or Mac.

If you forgot your iPhone passcode - Apple Support

If you have a backup of the phone, you can use the backup to restore the data on the phone during the new setup. Otherwise, the phone will look like it did when you first purchased it.

If this all sounds a bit too intimidating, make an appointment to visit the Apple Store or an Authorized Apple Servicer.

Backups must occur before catastrophes. After a catastrophe it’s too late.

Backup methods for iPhone, iPad, and iPod touch - Apple Support

That depends on whether the iPhone is operating normally, or it is already locked. If it is already locked, it's too late to back up.

Jeneknifer wrote:

Can I back up my iPhone before I restore it?

Certainly, assuming you can access your iPhone (know its passcode, etc.)