iPhone passcode entry screen hangs on two-factor authentication setup

Hi, I've just updated my Macbook Air to High Sierra, & set up two-factor authentication. While it appears to have worked & both my devices - laptop and iPhone 5c - are recognized in my account, on the phone itself the two-factor authentication setup went as far as inputting my device passcode, and then just hangs. Waiting does no good, up to 45 min. Once I'm in the hung screen, I have to reboot the phone to get out of it. Other than this though, authentication appears to work. Phone is running 10.3.3.

I don't know where to go from here. Has anyone else run into this? Is there a fix?