Does this number belong to you? If not, then the simple answer is that you don't. It is illegal and is just not worth doing the jail time or paying the fine for.
Of course if the number is yours there are many way to look at the history which usually involve logging into your account either online or through an app on your phone. It really depends which network you are, so your first port of call should be your carriers website.
Even if you haven't set up an online account - or if you've forgotten your details, most carrier's websites have helpful contact links for just those kind of scenarios!
If the phone does belong to someone else, a partner perhaps, it is always worth talking to them and asking the question outright. You can usually tell if someone close to you is telling the truth. To go behind their back and look at their private information gives them a counter argument if you do find something to accuse them of.
