You can always answer another phone call while on a video call on Instantgo. You will be able to resume your call when you finish the other one.
Still, be mindful of the following item when you pick up another phone call while on a video call:
The image or feed of the video will froze as you won't be actively on the Instantgo application. The image might remain frozen even when you get back on the call forcing to hang up and restart the call to resume the live feed.
The other user might get disconnected.