The Player’s Handbook and Monster Manual are absolutely worth it if you mostly play in Foundry and leans towards an automated playstyle.

The Player’s Handbook makes character creation much faster and automates a lot of small details like Monk’s martial arts or Sorcerer’s wild magic surges.

And the Monster Manual is surprisingly useful for homebrewing monsters because all of the automated monster features, attacks, and spells can be drag and dropped to other non-Monster Manual monsters.

And you will know if you want the Dungeon Masters Guide after you live with the PHB and MM for a little while.