I resolved this by moving phone to my ubuntu 18 laptop. i had to add the USB device per this page: https://android.stackexchange.com/questions/144966/how-do-i-get-my-device-detected-by-adb-on-linux

Started ubtouch and it's now installing.

OnePlus one connected to OS X. Trying to install ubports, but i can't even start. I get the error "Please reboot to bootloader". I hold power button and volume up for a long time and nothing happens. Can anyone recommend anything to try?