How do I play audio on my ZTE phone through Bluetooth without my dial/phone call from taking over?

So here is what I want to do , I want to be able to access my voicemail and use my Bluetooth speaker to still play audio from my phone while I use that audio to record my greeting. I want to do this because I am tired of robocalls so I want to record a 5 minute greeting of nothing but music. I have disabled my... show more So here is what I want to do , I want to be able to access my voicemail and use my Bluetooth speaker to still play audio from my phone while I use that audio to record my greeting. I want to do this because I am tired of robocalls so I want to record a 5 minute greeting of nothing but music. I have disabled my Bluetooth from taking over phone calls but when I access my dial pad and get in my voicemail. it still takes over my Bluetooth speaker