Matt_M thanks for the reply but unfortunately neither of the referenced links offer much detail nor does this appear to be answered yet.
The problem has been well described in another support thread (iphone 6 - restart screen with apple logo randomly appears during phone calls) albeit with an iphone 6. However the symptoms are exactly the same.
Using an iPhone 5 with IOS 8.0.2:
While on a phone call using headphones with the phone laying on a desk, the call will go silent for 4-5 seconds while the apple logo appears on the screen (just as though it had been restarted). However, after 4-5 seconds the phone call will resume. The call is not disconnected nor has the phone rebooted, rather to the caller on the other end of line it appears as though they've been muted.
It happens intermittently but was not experienced prior to updating to IOS 8.0.2
I've reset the network settings (under Settings | General) and restarted the phone but this hasn't solved the issue.
Is this an indication that SpringBoard is abending and restarting during calls?
Any guidance on resolution would be appreciated.