The phone will need to be completely erased, but can be restored if there is a backup. You will need to get the Apple ID Password by using one of the steps in this support article and is simple if your phone has been listed as a Trusted Device or has your phone as a Trusted Phone Number.
If you forgot your Apple ID password - Apple Support
With the Apple ID Password, you can reset the Passcode used to login without using a computer, by following this:
If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support
If you are unable to reset the Passcode by following that article, then you will need to use a computer, to reset the passcode:
If you forgot your iPhone passcode - Apple Support
If you do not have a computer available, you can get assistance from Apple and they may be able to help with the process. They will not be able to reset the device without erasing it and will not be able to recover the forgotten password without following those steps. They are helpful and may be worth a visit, but there are no shortcuts and something you can do yourself.