no trick or magic, you gotta learn everything. Else, you might be able to find a special tutorial that exploit a vulnerability with all the details on how to exploit it. Honestly, you shouldn't dive into it unless you know what you are doing.
Start by learning recon, majority of ANY hack should be spent on recon.
Asking how to hack that is like asking what tools do I use to build a bridge. There are a ton of variables that could go into it. Like Defalt said learn recon. Is the phone an android or iphone? if it is an iphone is it jailbroken? is SSH enabled? you get the point.
Ok let me tell you one thing.iphones can't be hacked unless its jailbroken.