Phaeton was powered by four Parsons steam turbines, each driving one propeller shaft, which produced a total of 40,000 indicated horsepower (30,000 kW).

The turbines used steam generated by eight Yarrow boilers which gave her a speed of about 28.5 knots (52.8 km/h; 32.8 mph).

[5] The main armament of the Arethusa-class ships was two BL 6-inch (152 mm) Mk XII guns that were mounted on the centreline fore and aft of the superstructure and six QF 4-inch Mk V guns in waist mountings.

On being commissioned, she was assigned to the 4th Light Cruiser Squadron of the Grand Fleet, and between February and March 1915 was operating in the Dardanelles in support of the Allied landings at Gallipoli.

On Phaeton's return to home waters, she was assigned to the 1st Light Cruiser Squadron of the Grand Fleet and by mid-April 1915 she was operating out of Scapa Flow.