Q: Is there any way to determine if your iPhone has been compromised?
A: Not for normal people.
The "typical" symptoms listed on the web are unreliable.
And the software tools that detect jailbreaking are easily fooled and unreliable.
Q: Is there any way to "de-compromise" your iPhone?
A: A factory reset (IOS reload) will fix software compromises that reside on the phone.
Hardware compromises require a new phone.
Network compromises require a new carrier.
Q: If the only way to fix things is to reload the iPhone's IOS (operating system), what's the best way to save all of your content (Apps, Photos, Music, and Contacts) and then reload it later?
In the future, never leave the phone unattended
and never loan it to anyone.
And/or plan on frequent OS reloads.
According to the link above it doesn't seem to ridiculous anymore, especially when they hold conferences showing how to do it.