How can I know if my phone was hacked ?

Yes it can my phone is hacked it takes pictures when it wants to all by itself it also shows other peoples email accounts in settings where it says to edit reachable at and my email accounts dont sync at all with my emails and says password incorrect when they are correct it costing me thousands in lost business because my business emails never come to me

You did the right thing with changing your password. You might want to enable 2 factor authentication if you haven’t yet.

A non-jailbroken phone cannot be hacked. Why do you think your phone was hacked?

Unless you jailbroke your phone, it wasn’t hacked. Your Apple ID and iCloud account were probably compromised. Change your password and enable 2 factor authentication.