Well, not only if your phone is in a call, but also your phone number, device id and the number of the person you're connected to.
Read phone status and identity:
Allows the app to access the phone features of the device. This permission allows the app to determine the phone number and device IDs, whether a call is active, and the remote number connected by a call.
And don't worry if your friend has the Facebook app and calls you if you don't have a profile. They can just search through your friend's contacts to associate your number with a shadow profile of you anyway.
Read phone status and identity: Allows the app to access the phone features of the device. This permission allows the app to determine the phone number and device IDs, whether a call is active, and the remote number connected by a call.
https://play.google.com/store/apps/details?id=com.facebook.k...
And don't worry if your friend has the Facebook app and calls you if you don't have a profile. They can just search through your friend's contacts to associate your number with a shadow profile of you anyway.