Player handbook add to current game

I recently started a curse of strahd game and just got the players handbook. How do I add it to game?

You don't have to "add" it.  The content of PHB will already be in your compendium.   If you're the DM and want to share that compendium with the players though, you'll have to set that in Game Settings.

ya I do want to share and it says I have slots to share but when I hover over it there is only a red circle with a red line through

You'll probably want to review the wiki page on compendium sharing .  Not sure if this is your issue or not, but one of things is: Plus Subscribers  Roll20 Plus subscribers may purchase any compendium. They may share their purchased compendiums with three active games that contain no more than themselves plus 10 players each (11 total per game).

Ive one game with five players so thats not it...

Have you set that particular game to use the 5e compendium? Usually it is set by virtue of the character sheet you use, but it's a possibility to check out.

HI there. I have acces in game compendium set to 5th edition d&d. below that I have share with my players? yes. Then it has available compendium slots the first one has curse of strahd then the following two say "compendium sharing slot available". if I hover over the sharing slots I get a red circle with a red line through...even when I save changes the compendium does not seem active in my strahd game which I want it for!  Also thank you both for your help! I appreciate it!

Hi there. I want to thank you all for your help but I just logged in again and its working now! the wonders of technology!  I do appreciate your help!