Hi Akabueze!
For iPhones, the process is harder, because Apple does not let its users to install applications outside the App Store, so what you can do in case of iOS is to try and scan it as shown in section 10 to check if it has any vulnerable service on open ports using Zenmap or any other vulnerability scanner, though I don’t think that you will get that much from the scan results if the phone wasn’t jailbroken, but it’s worth to try and see. Also, if the iPhone was jailbroken, then the procedure will be a lot easier (Take for example the SSH service running on port 22 with a default password of Alpine). There are other social engineering techniques that can be used to gain access, but they’re not very realistic and it’s not worth even to try them sometimes.
Hope it helps!
Diego