Note that I'm saying the following as a player who absolutely adores this game and just wants it to be the best it can be:
Honestly the phone system needs to be reworked, if not entirely scrapped. It simply isn't fun in any way whatsoever, it isn't being developed and even if *finished* it simply won't be worth all that development time which could just be used to develop more actual plot instead. You have basically a perfect AVN formula here already, the phone system is in practice like introducing a sandbox element for no reason that just ruins that formula. You're not going to use it to offer any meaningful choices anyway, it's already just going to be a case of "You should make this call at this point in time to progress this particular plotline" and when it's something that linear just use normal dialogue for it, so at least people won't randomly miss it. If those plotlines are supposed to be optional, just make them optional through dialogue like everything else. Hiding content in a system that players risk clicking past is just not a good idea at all.
I understand the impulse to introduce these additional systems and the stray thoughts that say that just having your game be a normal VN is "too simple" but that's just not the case, VNs are simply already perfected as a format, tacking on additional systems on top of them just ends up making everything worse 9 times out of 10, conservatively.
I'm saying this now because I had to start the game from scratch because of save game issues and I've just been skipping past everything and the phone scenes are just a nightmare in this case, but even last update when I started playing the game I distinctly remember feeling it was just a bother every time the game said "Phone unlocked" and I had to mindlessly click each name in the phone to see which person I was supposed to call.
Even if the phone system was finished and worked perfectly exactly like you wanted it to, it's simply not going to be fun. Not a single player is going to go "Wow, this is just like a real phone!". It's not going to be immersive, it's not going to make the game better. These kinds of extraneous flourishes simply isn't what players actually want. Anything that makes the game more difficult to navigate than it needs to be is just a nuisance. You've already got a great AVN that does a very good job (other than this one exception) of focusing on what matters: building story and lewd scenes. You're great at making both of those things. You pull them off incredibly well. There doesn't exist a reason to try and do these extra systems, and more than enough reasons to NOT do them.
If any of this sounds like me hating on the developer, that's not my intention at all, I just get way too passionate over game design and tend to ramble on. Any "hate" I have is exclusively aimed at the phone system, NOT the developer.