Short answer, yes you can get a virus by connecting your phone to your computer by usb. In fact one of the most common ways to get a virus is through the use of a USB thumb drive. Often workers in the factories in China and Taiwan are bribed to install malware on the drives on the line. So unsuspecting user goes and buys one from favorite electronics store, goes home, plugs it into their computer and infects their system as it bypasses the firewall.
And you can have PC malware laying dormant on an Android phone laying dormant waiting to be connected to a PC.
And you can have PC malware laying dormant on an Android phone laying dormant waiting to be connected to a PC.