A downhole fluid separator, comprising: a first tubular comprising a volume defined between an open, uphole end of the first tubular opposite an open, downhole end of the first tubular, the volume of the first tubular comprising one or more baffles configured to separate a mixed-phase fluid into separate flows of the gas and the liquid, a fluid pathway configured to receive, at the open, downhole end, the mixed-phase fluid from an annulus of a wellbore and provide the separated flows of a gas and a liquid to the uphole end of the first tubular; a second tubular comprising a volume configured to receive at least a portion of a downhole artificial lift device through an open, uphole end of the second tubular opposite a closed, downhole end of the second tubular, and an adjustable opening formed in a portion of the second tubular at a location between the uphole and downhole ends of the second tubular and configured to selectively receive the flow of the liquid from the annulus of the wellbore into the volume of the second tubular by selectively fluidly coupling the annulus of the wellbore with the volume of the second tubular; and an actuatable wellbore seal positioned around each of the first and second tubulars and between the first and second tubulars to radially surround the first and the second tubulars, downhole of the adjustable opening, and between the uphole ends and the downhole ends of the respective first and second tubulars so that, when actuated, the actuatable wellbore seal fluidly isolates an uphole portion of the annulus from a downhole portion of the annulus. a first tubular comprising a volume defined between an open, uphole end of the first tubular opposite an open, downhole end of the first tubular, the volume of the first tubular comprising one or more baffles configured to separate a mixed-phase fluid into separate flows of the gas and the liquid, a fluid pathway configured to receive, at the open, downhole end, the mixed-phase fluid from an annulus of a wellbore and provide the separated flows of a gas and a liquid to the uphole end of the first tubular; one or more baffles configured to separate a mixed-phase fluid into separate flows of the gas and the liquid, a fluid pathway configured to receive, at the open, downhole end, the mixed-phase fluid from an annulus of a wellbore and provide the separated flows of a gas and a liquid to the uphole end of the first tubular; a second tubular comprising a volume configured to receive at least a portion of a downhole artificial lift device through an open, uphole end of the second tubular opposite a closed, downhole end of the second tubular, and an adjustable opening formed in a portion of the second tubular at a location between the uphole and downhole ends of the second tubular and configured to selectively receive the flow of the liquid from the annulus of the wellbore into the volume of the second tubular by selectively fluidly coupling the annulus of the wellbore with the volume of the second tubular; and an actuatable wellbore seal positioned around each of the first and second tubulars and between the first and second tubulars to radially surround the first and the second tubulars, downhole of the adjustable opening, and between the uphole ends and the downhole ends of the respective first and second tubulars so that, when actuated, the actuatable wellbore seal fluidly isolates an uphole portion of the annulus from a downhole portion of the annulus.