If the audio device such as headphones or speakers is "multipoint" it should be able to support two Bluetooth connections simultaneously switching seemlessly between the two. A modern phone being a master device can theoretically handle up to seven bluetooth connections although hardware limitations can reduce this dramatically. My own experience is that Bluetooth has been a flaky system since it's outset and I still get reconnection issues to this day with just one connection.
Ironically my budget bike reliably supports two Bluetooth connections from phone, one to its TFT screen for mapping/position, the other to helmet audio system for voice instructions, music streaming or phone calls.
