Backup and update

So, I am trying to backup my iphone to my macbook pro and it says it can't because the phone is disconnected, even though it is clearly not. So I thought maybe I had to update everything. So, I fully updated my laptop and its itunes, but then i tried to update my phone, and when I try to install 11.2.6 it says there is an error. I did as support said and tried to check for an update on itunes, to which it told me 10.2.1 was the most current update even though it obviously isn't. I just want to back up and restore my phone but literally nothing is working for me can i get some help here???