There are so many recipes with minor variations. In the end it doesn’t matter much except for some points I’ll mention. Here is a random one. https://www.vickypham.com/blog/vietnamese-beef-noodle-soup-pho-bo

I would say that a lot of the cooking process is hard to explain via a book. Videos are good. This one seems to be done by a very knowledgeable woman. https://youtu.be/xxM4t8vP-0A

After skimming the above video I’m really impressed by that woman’s knowledge. One thing i am not sure she discusses is the process of skimming the fat off the broth.