Q: iPhone will not connect to Wi-fi at work

The iPhone should be able to connect to the secure network, as well.  See the "Connect to a secure Wi-Fi network" section in:

Connect to Wi-Fi on your iPhone, iPad, or iPod touch - Apple Support

Terry Brown wrote:

 

At work (school system), we have a network (with login) and a 'guest' network. My notebooks generally connect to the 'secure' one (the MacBook Pro more reliably than the MacBook) -  my iPhone will only connect to the 'guest' network. Is this by design? Is there a fix?

What does the IT people at your work (school system) say about it?

Try resetting the network settings on the iPhone:  Settings > General > Reset > Reset Network Settings. Then try joining the secured network again.