Q: Audio streaming to two device (speaker)

Hi zzuzu,

Although you can pair your iPhone to multiple [audio] devices, you can only use one device type at a time.

Set up and use third-party Bluetooth accessories - Apple Support

Play audio to a Bluetooth accessory

If you want to play audio to a Bluetooth accessory, you'll need to select the accessory.

You can do this by using the AirPlay option in Control Center. 

 

While on a call you can tap audio and select the device that you want to use.

Note if you have multiple Bluetooth audio accessories, you choose which one you want to hear at the time.

Take care.