Playing voicemails through bluetooth

Ok, so all of my work voicemails are emailed to me. When I am in my car with Bluetooth connected it won't play the voicemail thorough my speakers all of the time. Sometimes it does and sometimes I can see the message playing but it is not coming through the speakers in my car or on my phone. In the past there was a button on the play screen on my phone that let me select Bluetooth or my phone but that is not there anymore. Any ideas how to make this work consistently? Thanks.