You can use a Bluetooth receiver to do what you’ve described. Here’s one that should work:
https://smile.amazon.com/dp/B00YPATOEE
You’ll also need a splitter to go from the Bluetooth receiver to your car stereo and your amplifier. However, a much better solution would be to use a high-to-low-level adapter that connects your car stereo to your amplifier. You can attach the hi-to-lo adapter to either the front or rear speakers, or to the speaker wires coming from behind the car radio. An adapter like that will be a cleaner solution and also allow you listen to your sub with the radio or anything else playing from your car’s stereo.
Here’s an adapter that should work with your amplifier: https://smile.amazon.com/dp/B001EAWS3W
And you can still use the Bluetooth adapter listed above to connect your phone to your car stereo wirelessly.