You might want to consider shutting off your FaceTime for a little bit. A bug which has come to light over the past few days exists at the present moment that would allow anybody who has your phone number and an iPhone to begin eavesdropping on your through your iPhone without you knowing it.
Here's how it happens...
1) Start a FaceTime Video call with an iPhone contact.
2) Whilst the call is dialing, swipe up from the bottom of the screen and tap Add Person.
3) Add your own phone number in the Add Person screen.
4) You will then start a group FaceTime call including yourself and the audio of the person you originally called, even if they haven’t accepted the call yet.
Here's a video which shows this bug in action...
In a statement, Apple said that their engineering teams were aware of the issue and have "identified a fix that will be released in a software update later this week."
For now though, you might want to consider hopping into your FaceTime settings on your phone and toggling the old FaceTime functionality off until the problem is fixed.
Here's that process if you feel so inclined...