Not at all. I used Google Maps on my Samsung S8 in the case for 4-6 hour stretches at a time, whilst it was plugged into a mobile battery pack, and it didn't over heat once.
It is a bit difficult to hear the call through the case, even on loudspeaker. If you unclip the case and open it you can hear much more clearly. If you use headphones you can hear the call, but it may be difficult for them to hear you unless you open it. I hope this helps.
With phone screen on for extended periods (hours), do phones tend to overheat inside this case?
Not at all. I used Google Maps on my Samsung S8 in the case for 4-6 hour stretches at a time, whilst it was plugged into a mobile battery pack, and it didn't over heat once.
Do you think you could make a phone call with it in the case. ?
It is a bit difficult to hear the call through the case, even on loudspeaker. If you unclip the case and open it you can hear much more clearly. If you use headphones you can hear the call, but it may be difficult for them to hear you unless you open it. I hope this helps.