|You are legally entitled to your privacy and Apple does not allows this kind of irregular apps on an iPhone or other device. Also every app installed is visible on the device itself or using iTunes. This is unless you have a jailbroken iPhone and someone did it for you. You can be sure about all this if your iPhone connects successfully with iTunes. If your iPhone is not recognized by iTunes it may be jailbroken, but again, fortunately you can Restore your iPhone to secured factory settings.|
a) If your iPhone is successfully recognized by iTunes you can do this:
Step 1 Connect your iPhone to the computer you use to Sync with (You use a computer with your iPhone, right?). Wait for it to appear under DEVICES. When it does you can check on the Summary tab the current OS. The top box says iPhone. Name, Capacity, Software Version... If you can't see "software Version" click on the "Build Version" text. It will toggle both options.
Step 2 Click on the Apps tab and you will find there a list of all available apps installed. The ones that are installed appear checked. Uncheck what you don't use and leave only what you are sure you need and press "Sync". Wait for the process to end and you will be done. Just disconnect the iPhone from the computer.
b) If you connect your iPhone to the computer you use it with (the computer with the active iTunes account) and it does not recognize it or it ask you to erase and Restore the device, this iPhone may be jailbroken. Well, you have the option to set it back the way Apple intended so no one can disrupt your privacy.
Step 1 Be sure you have a valid iTunes account under your name and with a valid password. If you don't have this, you may be using this device but is not actually under your control. In this case this is not technically "your" iPhone. (This situation is beyond my expertise and advise).
Step 2 If you have a valid iTunes account under your name, then the device is yours to set it up as you want. I am telling you this because without a valid password you can do very little or nothing to set it back to secured factory setting. Follow the link below to the Restore procedure.
You always have the option to buy a new device you will keep under your control.