As of today Remote Assist Mobile only uses the phone speaker or a connected cable headset.

Suggestion: Provide a button similar to the Teams app that allows the remote user to switch to loudspeaker or a connected Bluetooth device. This makes sense in noisy environments but also in situation where other people should not hear the communication with the expert (for example in a hospital).
Ideas Administrator

This feature has already been built for Remote Assist Mobile.  We are investigating the bug that's stopping it from functioning in some cases.
Thank you for the feedback!