A centrifugal well fluid pump has a pump intake and a pump discharge conduit extending upward from the pump. A barrier between the motor and the pump intake seals to casing in a well. A bypass tube extends from below the barrier, alongside the pump and has an outlet at an upper end of the pump. A riser surrounds the pump discharge conduit, the riser having a riser inlet in fluid communication with the bypass tube outlet. Liquid portions of the well fluid flow upward through the riser to discharge from the riser outlet and flow down to the pump intake. Gaseous portions of the well fluid flow upward through the riser and continue flowing upward into the casing.