How do I turn on auto answer calls only when connected to a Bluetooth headset?

Actually I found the option where i can turn on auto answer and select duration after when the call will be received, thats fine. But I dont always need my phone to auto answer. I need it only when I’m on a Bluetooth headset and riding my bike. There is an option called auto routing the call, which is not what im talking about. By the way, i have an android phone which has the option to select when I need the auto answer option to activate. So, my question is, whether im not finding the option or iphone really missed it out?