There seems to be a few ways to look at this.
I bought it, so I own it and can share with anyone I want. This is basically pirating and is frowned upon, regardless if for private use. Like Napster and their problems
I'll just share it and if we use it, then I will have them buy a copy. This is better, kind of like a lot of people do with DMsGuild. I would likely lean this way myself and have the player read some of the rules and see if they like it.
All the players buy a copy of PHB, so yeah, go buy your own. I would see this if everyone is on board to play with it. Does everyone at the table have Tasha's or Mordenkainen's? Usually not everyone, but one or two of the books are shared, but not copied. Not sure on digital book subscriptions for places like D&D Beyond, but PDFs have been a debate for a while.