Study and Performance of Phase Shift in Low Pass Filter

So far we have discussed the way in which a filter modifies the amplitude of the various frequency components in a signal. However, reactive circuit elements always introduce phase shift in addition to amplitude effects.
The concept of phase refers to the value of a periodic signal at a specific moment within a cycle. Thus, when we say that a circuit causes phase shift, we mean that it creates a misalignment between the input signal and the output signal: the input and output signals no longer begin and end their cycles at the same moment in time. The phase shift value, such as 45° or 90°, indicates how much misalignment has been created.
Each reactive element in a circuit introduces 90° of phase shift, but this phase shift does not happen all at once. The phase of the output signal, just like the magnitude of the output signal, changes gradually as the input frequency increases. In an RC low-pass filter, we have one reactive element (the capacitor), and consequently the circuit will eventually introduce 90° of phase shift.