Can an iPhone be hacked??

FYI, non jailbroken iPhone cannot be hacked remotely.

Best you change your Apple ID's password to something stronger (more than 8 characters + numbers + capital letters)

Follow the steps here: Change your Apple ID password - Apple Support

Jailbroken means the iPhone operating system (iOS) is modified.

To do that one need to physically do it on the iPhone.

You can start fresh by setting it to new. (You lose all the data though)

Read here: https://support.apple.com/en-us/HT201252

The symptoms you describe sound like a failed digitizer. If it occurs only when the phone is plugged it, the cable may be bad.

If he never had possession of your phone it is not hacked. But if you have any doubts at all do a DFU restore of the phone:

• Note that you must have a computer running Windows 7 or later, or Mac OS 10.9.5 or later
• Install the latest version of iTunes (12.7.4 as of May 2018) on your computer if it isn't there already
• Reboot your computer
• Disable any antivirus and firewalls
• Launch iTunes
• Connect the device cable to a USB port on the computer (not to a USB hub), but DO NOT CONNECT TO THE DEVICE YET
• Press and hold the HOME and SLEEP buttons (VOLUME DOWN and SLEEP on iPhone 7/7+) at the same time for 8 seconds, until the screen turns black, then release the SLEEP button but continue holding the HOME/VOLUME DOWN button. If an Apple logo appears while holding both buttons you held for too long; start over.
• While still holding the HOME/VOLUME DOWN button connect the other end of the cable to the device
• You should see a message in iTunes saying a phone in Recovery mode has been detected (it may take up to a minute for the message to appear). When you see that message release the HOME/VOLUME DOWN button and the device should restore. When asked DO NOT restore a backup; set up as a new phone.