Invasion of privacy

If you're concerned about your Apple ID being hacked, make sure to enable Two-Factor Authentication.

Two-factor authentication for Apple ID - Apple Support

Make sure that you read the entire document carefully before implementing it. Make sure to add additional trusted devices or numbers. Make sure not to delete the confirmation email. Once you enable 2FA, you will have 14 days to turn it off and it can only be done through the confirmation email.

It is extremely unlikely that any one is getting into your iPhone. The FBI is have difficulty. Especially if you apply the iPhone updates and are running on a recent model iPhone.

However, it is more likely someone could access online accounts.

Change your iCloud account password and enable 2-Factor Authentication.

If you use other online services, such as gmail contact service or calendar service or any other service, for contacts, calendars, pictures, etc..., then check with them on ways beyond changing your passwords.

Also, most online services store your data in such a way that law enforcement can get a warrent and gain access to anything you store on an online server.