As different external hard drives have different level of power consumption, they may not get enough power if two or more are used at the same time, therefore we don’t recommend using two external hard drives at the same time. You can charge your phone with the hub, but as the hub is not designed to charge mobile phones, the charging speed may not be very fast. The display resolution is not affected by the connected USB devices, so yes, you can still use HDMI at 4K 60hz