Federal prosecutors regularly use call records like this, to show that the people using the phones were involved in a criminal scheme.
That's why the cooperation of Cohen in this matter would be so important to make a case against others.
So why wasn't Trump charged? DOJ has a policy against indicting a sitting president. And it's worth noting that we don't know what Cohen told SDNY.
As for Hope Hicks, even putting aside the issue with Cohen, one likely reason why she wasn't charged is that the campaign finance laws require that she *knew* this scheme violated the law.