How to force Siri to use ONLY internal microphone I have a Bluetooth receiver in my car for playing music from my phone. It's great for that. But also has a microphone that sucks. 

My iPhone 7 automatically pairs with the device when I get in the car so I can listen to music. But when I go to Siri (by holding the home button down -- I don't use Hey, Siri) it is routed through that crappy microphone and therefore never understands what I'm saying. 

I finally figured out that I can enact Siri, then click on the little button on the lower right (in the 'Siri View') and be given a choice of what microphone to use. I can go back to internal and all is right with the world. But... then next time I get back in my car it's all reset over to the crappy microphone again and I have to go through the process to get it back to internal. 

This is crappy. I like using Siri when I drive and the iPhone's microphone isn't too bad in picking up my voice. How do I ALWAYS keep Siri coming through my device's microphone instead of constantly resetting back to an external Bluetooth one?

Much obliged to whoever has figured this out and willing to share:)
This is an often-asked question on many sites.  Unfortunately, all those sites say the same thing: this isn't possible.

As long as you're connected to a Bluetooth device that has a microphone, the iPhone will use that mic for Siri unless you specifically change it (like you mentioned) each time you use it.  I think your best option is use a Bluetooth device that doesn't have a mic.  No mic, no problem.

I don't know if this is part of the Bluetooth specifications and can't be changed or if it's an Apple-controlled thing.  I would recommend providing feedback to Apple and letting them know this is something you want.