Audio support in ROS is pretty thin on the ground, but there are a few packages that will bind gstreamer pipelines
This ROS1 package looks like it would be pretty easy to port to ROS2:
http://wiki.ros.org/pocketsphinx
Otherwise, a riff on gscam might be doable, the pocketsphinx pipeline is pretty simple.
gst-launch-1.0 autoaudiosrc ! audioconvert ! audioresample ! pocketsphinx ! fdsink fd=1
I’d love to plug my own ros-gstreamer package, but it doesn’t support string payloads yet.