Such a hasty generalization. It's not that we don't care about PHY, but expecting in depth PHY treatment in modern networking book is like expecting semiconductor physics in the The Art of Electronics book [1]. Personally PHY is my passion and trying to propose a new reliable PHY waveform to 5G and upcoming 6G standards.

Modern PHY is like bit twiddling in programming, 99% programmer don't do it and don't care unless you are doing HPC or device driver. In networking those who're doing PHY belong to communication engineering field. For modern networking the relevant PHY mostly dealing with digital I/Q signal for wired/wireless and there are many excellent books on the subject such as this [2].

[1]The Art of Electronics (2015):

https://news.ycombinator.com/item?id=38748370

[2] Digital Signal Processing in Modern Communication Systems

https://www.amazon.com/Digital-Signal-Processing-Communicati...

This is an excellent book on learning DSP for modern wireless communications and it should get you over the fundamentals [1].

There is an interesting project for open source LoRa physical layer implementation in GNU Radio. The authors had to reverse engineer the LoRa physical layer for the implementation because it is proprietary unlike the data link layer LoRaWAN part of it [2].

[1]Digital Signal Processing in Modern Communication Systems:

https://www.amazon.com/Digital-Signal-Processing-Communicati...

[2]LoRa PHY based on GNU Radio:

https://www.epfl.ch/labs/tcl/resources-and-sw/lora-phy/