Phone privileges are just that, privileges. It will vary from week to week. It will vary from company to company. If they do something wrong, they can lose their phone privileges for the week. If they do something well, they may get extra time. It's impossible to predict. It is not a guaranteed minimum like during Indoc. Things will gradually start to loosen up. But the timing will depend on many factors.
I know it's hard. Believe me, I've been there. And I've got a DD who refused to let me friend her on Facebook and doesn't write emails. This is practice for when they are at sea for months on end and you hardly ever hear from them. This is nothing compared to facing A split and knowing you won't see your DD for two consecutive holiday seasons. The best thing you can do is find something to keep yourself busy so you are not obsessing over every possible phone call. Go to church! If they can't get through, they will most likely get to call again a little later. But please don't spend all of your time hanging anxiously by the phone. It really only breeds more anxiety.
Take a deep breath and know that you did a great job preparing them to be strong, independent young people. They're fine and you will be too, even if it doesn't feel like it right now.