How do I refresh the devices in Image Capture?
If you quit the application and re-start it, that seems to resolve any devices that connect and get missed when you plug them in after the application has launched and enumerated the connected USB devices.

Even if you have iTunes and Xcode and other apps running, I've not seen Image Capture fail to recognize connected devices if you restart the program and I have certainly seen it miss device connects on occasion when other apps are running and want to talk with an iOS device.

That being said, here are things to check:


Different USB ports and cables
Trust setting on the iOS device (Settings -> Reset -> Reset Location &amp; Privacy.)
restart either the phone or the Mac or both
update software on the phone or the Mac or both (iTunes updates install sync software and drivers needed)
make a new account on the Mac (to test once)  in case image capture or your photo library settings or data are corrupt 


See https://support.apple.com/en-us/HT202778 for trust issues and iOS.