The replacement for the Silver Ghost was initially called the New Phantom, but became known as the Phantom I after the introduction of the Phantom II. A little larger and naturally more modern car than its predecessor, the chassis and engine design were similar to the Ghost but with a detachable cylinder head. This was equipped with pushrod-operated overhead valves. The gearbox remained a separate unit but now with a plate clutch instead of the earlier cone type.

Production numbers
1925 - 1929
6 cylinders, capacity 7668cc. Pushrod-operated overhead valves. Twin cylinder blocks on an aluminium 2–piece crankcase. 7 bearing crankshaft with vibration damper. Single detachable 12-plug cylinder head, initially cast iron (CR 4:1) with all plugs on the nearside; aluminium from 1928 with 6 plugs per side (CR 4.2:1). Pressure fed lubrication by gear type pump. Oil capacity 12 pints.
R-R 2-jet type with automatic air valve and starting carburettor.
Independent magneto and coil, each firing 6 plugs.
Cooling system
Vertical radiator shutters operated by hand. Fan and centrifugal water pump.
Fuel system
18-gallon rear tank and Autovac. Direct-acting gauge on tank superseded in 1927 by a Hobson Teleguage on the dashboard.
Separate unit 4-speed gearbox with a single plate clutch. Torque tube. Right hand gearchange. Rear axle ratio 3.47:1 (from 1927 optional 3.25:1)
Leaf springs. Semi- elliptic front and cantilever rear. Friction shock absorbers initially, changed to hydraulic at the front 1926 and the rear 1927.
Internal expanding 4–wheel operation with independent handbrake on the rear wheels. Mechanical servo driven from the gearbox.
Steering box
Worm and nut.
Chassis lubrication
By oil gun.