Trouble with iPhone accepting my passcode

Not likely, since you would need the passcode in order to do a backup.

Forget Passcode or Restore Device

1. If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled
2. How to erase your iOS device & then set it up as a new device or restore it from backups

For help with the above or later models including iPhone 7, 7s, 8 or later, iPad Pro 11" and iPad Pro 12.9" models please refer to If your iPhone, iPad, or iPod touch won't turn on or is frozen.

If the above doesn’t work for you, then:

Follow these steps to place your iOS device into recovery mode: iPhone DFU mode explained, and how to enter DFU mode on your device.

If all fails then make an appointment at the Apple Genius Bar for service. If you need to find an Apple Store - Find a Store - Apple. If you did not purchase it from Apple then you will need to look to the vendor for service.

If iCloud Backup is enabled, connect it to a charger. And if it's connected to a Wi-Fi network, it should create a backup.

Also, if you have ever synced your iPhone with iTunes, you cant try to create a backup on your computer.