Frequency response of a series RC circuit
Firstly,
The plots and the RC circuit doesn't match.
The plots are for LPF and the RC circuit in the picture is HPF.

Secondly, coming to the answer.
Based on the operating frequency, the transfer function of the system alters the magnitude &amp; phase of the incoming signal.

If \$V_{\text{in}}, \theta_{\text{in}}\$ is the input signal and
\$V(s),\theta(s)\$ is the system response to the input frequency.

then
$$V_{\text{out}} = V_{\text{in}} \times V(s)$$
$$\theta_{\text{out}} = \theta_{\text{in}}+\theta(s)$$