Is it possible to use the phone speakers for Siri even when Bluetooth is connected? I have my phone connected to a Bluetooth auxiliary adapter in my vehicle. Sometimes I have the audio source set to something else like CD or FM radio. The problem with this then is I hear no audio output when I need to use Siri. Is there a way to force Siri to use iPhone speaker by default even when connected to Bluetooth? I have an iPhone X.
No, you can't direct Siri to a different output than the default output.
If your iPhone is connected via bluetooth to your car stereo then that's where sounds will be directed.
Your options are to disconnect bluetooth from your car stereo or upgrade to a CarPlay-enabled head unit.