After you went to the gym and asked Phoenix to be Charlotte's bodyguard, go to your Home Entrance and you'll get a scene where you introduce Phoenix to Charlotte.
Then you can go to the Mall and you'll see that Phoenix do a great job as Charlotte's bodyguard. After that, go to the Yacht on Monday and make sure to fuck Charlotte in the ass to get Spitroast scene with Phoenix ( Repeatable ).
Last but not least, you can meet Phoenix and Charlotte shopping in Boutique Store and have a threesome scene ( Repeatable )