When electric current flow through our body, we experience an electrical shock. The electric current will flow through our body if the voltage is applied to our body. So, when we touch phase wire standing on the ground directly then a voltage is applied to our body, and current starts flowing through our body, and we experience the electrical shock.
Neutral is always connected to the ground or earth. So, the voltage at the neutral is always zero. So, when touching the neutral wire while standing on the ground there is no voltage applied to our body, therefore no current flow through our body and we do not get the electric shock. But the neutral wire should not have more resistance than the person's body.
Since the neutral is at the same voltage as the ground, both our head and our feet are at 0 V. So, the voltage across us is 0 V and therefore the current is 0 A.