You'd have to be extremely rich or someone at a very high level, such as a Senator, Congressman, Ambassador or similar for anyone to want to invest hundreds of thousands of dollars into hacking you. Translation, it's very hard and very costly to hack an iPhone which hasn't been jailbroken. Nothing you've described leads one to think you've been hacked.
Have you force restarted your iPhone lately? Are you using a Passcode and Find My on your phone? Are you using Two Factor Authentication on your Apple Account?
See how to Force Restart here --> Force restart iPhone - Apple Support
Are you running low in memory on your iPhone? That could cause a phone to run slow. Open the Settings App > General > iPhone Storage and see if you are running out of space. If you are, delete things you don't need or use, such as Apps, Photos, Music, Files, Messages, Email, Files.........