NR protocol stack - How do layers talk between gNB and UE?

Hello experts.
When I look at 5G protocol stacks I see arrows between the layers matching gnb to ue. For example in this figure, there is arrow from PHY from PHY from MAC to MAC from NAS to NAS.

Question, what do we mean by saying X layer on gnb talks to X layer on UE. Transmission over over the air is from PHY layer so I don’t understand how and what is meant by matching the layers?

Please any insights

The Data Flows from Top-down from UE, Lets take an Example of Uplink data sent by UE

  • UE Gets Data into its PDCP , PDCP adds Header and does ciphering
  • Data is sent to RLC , RLC Segments/Concatenate the data and adds headers
  • Data is sent to MAC, Fills the data as per the Grants received into Transport Blocks
  • Phy sends that over the Air via PHY Channels

at the Network

  • Network decodes the data over PHY Channels
  • at MAC, it receives data from MAC, MAC retrieves the data and sends it to RLC
  • RLC does concatenation if the data was segmented by UE, Removes RLC Headers
  • PDCP receives data from RLC, Performs deciphering, and removes PDCP headers
  • PDCP sends IP data to Upper layers

So the Line that you see between UE PDCP <—> NW PDCP, is the PDCP start, and endpoint

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Thank you very much