A circuit that contains pure resistance R ohms connected in series with a pure capacitor of capacitance C farads is known as RC Series Circuit.
V=rms value of applied voltage
I=rms value of the circuit current
The voltage across R, VR=IR where VR is in phase with I.
voltage across C,Vc=IXc where Vc lags I by 90°.
Taking current as references phasor.
The voltage drop VR=IR is in phase with the current and is represented in magnitude and direction by the phasor OA. The voltage drop Vc=IXc lags behind the current by 90° and is represented in magnitude and direction by the phasor AB.
The applied voltage V is the phasor sum of these two drops
Current I leads the applied voltage V by Φ°.
since the current is taken as the reference phasor, the negative phase angle implies that voltage lags behind the current. This is the same thing as current leading the voltage.