I have marked my phone on the list of usb-devices below guest window. On the phone I have selected "Transfer files" connection mode (as it should be if you run something from PC). But when I'm trying to run something from a guest to the phone:
error: insufficient permissions for device.
May be this is related.
Also shared folder doesn't appear on the guest: I tried to set mount point (not sure if this is obligatory, but tried) to guest's home directory. Guest extensions are installed and the user is in vboxsf group (on the guest).