The physical layer is responsible for –

The physical layer is responsible for the transmission of raw bits over a physical medium. It defines the electrical, mechanical, and procedural specifications for activating, maintaining, and deactivating the physical link between devices. This includes the transmission of data as electrical signals, light pulses, or radio waves.
Key responsibilities of the physical layer include:
Bit transmission: Sending and receiving individual bits over a communication channel.
Signal encoding: Converting data into signals suitable for the transmission medium.
Physical topology: Defining the layout of devices and connections.
The physical layer does not handle error detection, flow control, or addressing—these are managed by higher layers. It only ensures that bits are transmitted correctly over the physical medium.