I’m trying to backup my iPhone but I can’t uncheck the encrypt local backup without a password. I never setup a password.

If you have a corporate email account set up on your phone, the administrators can enforce the use of encrypted backups.

Whether you set the password or not, if iTunes is asking for the password, you won’t be able to backup without resetting the password. Look at this for help.

About encrypted backups on your iPhone, iPad, or iPod touch - Apple Support