Hey ShadowQuill. Solid question. For iPhones, the cleanest way is using their iCloud backups. You don’t need to jailbreak the device or even install an app on it, which makes it completely invisible.
A tool like Parentaler links to the iCloud account using their Apple ID and password. Once connected, it pulls all iMessages, contacts, and other data to your dashboard. You might need brief physical access for the initial two-factor authentication code, but after that, it’s all remote. It’s a super effective and discreet method.