The 5th chapter is packed but I don't see it as a bad thing.
As for the cell phone, I can say that prolly it was not a good idea to have two sex scenes playing out concurrently - one IRL and one on the phone. Having to constantly switch between them you lose focus and can't fully immerse into any of them. I later played the same scene with only Anon getting action and it felt better that way - I could fully concentrate on Cee, picturing the scene in my imagination, it felt more real, immersive.
I think it'd be better if the sharing scenes of the two couples followed one another instead of being simultanious - but I wouldn't call it a serious flaw. Just a point for improvement.