How to find spyware on my iPhone

If you suspect that your iPhone has been compromised I would recommend a DFU Restore which will replace the entire operating system and the device firmware as well which would get rid of any monitoring software. If you restore from a backup a piece of software being used to monitor your device could also be restored so to be sure manually reinstall applications you want from the App Store.

[1] DFU mode to Restore

You can do a search for the word Cydia.

Someone else would have had to have access to your iPhone for more than 45 minutes and known your passcode, Apple ID and password in order to jailbreak it. Did this occur?

If it has been jailbroken you need to put it in DFU mode (not recovery, Google it for a video how to do it) and then restore it as a new device.

Simple: do a restore as new.

https://support.apple.com/en-us/ht204184