iTunes can't see my iPhone (High Sierra)
For years I've had a 2008 Mac Pro (3,1) running El Capitan, with the iTunes media files on an external hard drive. I've set up a 2010 Mac Pro (5,1) running High Sierra and want to migrate everything to that machine and sync music to my iPhone SE. On the new machine, iTunes recognizes my media on the external hard drive, and also recognizes and syncs my iPod Classic when I plug it in via USB. But the iPhone is not recognized, regardless of whether I plug it into the USB port or use WiFi. Disk Utility doesn't show it, and of course the Finder doesn't show it, but System Information knows there is an iPhone plugged into the USB port -- however, iTunes sees nothing.
I've tried switching USB cables, USB ports, etc. I tried completely restoring the iPhone, but still it is not recognized in iTunes or anywhere else on the Mac. I have the latest system software on both the Mac Pro and iPhone. There's no security software on the Mac other than the built-in firewall and ClamXAV antivirus. Is there anything I can do to be able to sync the iPhone SE using iTunes on the High Sierra machine?
Mac Pro, macOS 10.13