Q.How could CE amplifier able to produce 180° phase shift?

In a CE amplifier the output collector voltage moves opposite to the input because of the relation between collector current and collector voltage. …

[!TLDR]

Output voltage falls when input rises (via $V_C = V_{CC} - I_C R_C$), giving 180° inversion.

In the common-emitter amplifier the signal is applied to the base and the output is taken from the collector. During the positive half of the input, the base current increases, so the collector current $I_C$ increases. This raises the voltage drop across the collector resistor $R_C$, and since $V_C = V_{CC} - I_C R_C$, the collector (output) voltage falls. During the negative half of the input the opposite happens and the output rises. The output therefore always moves opposite to the input, i.e. there is a 180° ph …