Switch USB ports + Try a different cable, my PH1 freaks out sometimes and refuses to work in fastboot mode and switching ports and/ or cables usually fixes, so try and switch ports and cables and then report back. Also, try to reboot bootloader as that has fixed issue similar to this on my phone as well.I have the drivers installed. This started after installing this Rom. Invictrix-mata-8.1.0-20180117-Official.zip.
Everything worked fine prior to this.