I often switch between phones and speakers, but I'm too lazy to do it through the sound preferences window. So I came up with this script*, and I'm sharing it here as others might find it useful.

You'll need to tweak it a bit to work in your machine, but once you do it you can run it from a launcher or a keyboard shortcut, it's really comfy.

Okay, here's the code:

#!/bin/bash

# You'll need to swap those four values with the ones that work in your machine.
# Check the rest of the post for further info.
mainCard="pci-0000_06_00.1"
mainProfile="hdmi-stereo-extra1"
altCard="pci-0000_00_09.2"
altProfile="analog-stereo"

# If the current default source is main, your new source is alt. Else, your new is main.
if [[ $(pactl get-default-source) == "alsa_output.$mainCard.$mainProfile.monitor" ]]
then declare -g newCard="$altCard" newProfile="$altProfile"
else declare -g newCard="$mainCard" newProfile="$mainProfile"
fi

# Tells PulseAudio to shift the card profile and default sink to the new.
pactl set-card-profile "alsa_card.${newCard}" "output:${newProfile}"
pacmd set-default-sink "alsa_output.${newCard}.${newProfile}" &> /dev/null\

# Tells PulseAudio to shift the currently running programs to use the new output.
for i in $(pacmd list-sink-inputs | grep index | awk '{print $2}')
do pacmd move-sink-input "$i" "alsa_output.${newCard}.${newProfile}" &> /dev/null
done

# Optional text notification.
if [[ $(pactl get-default-source) == "alsa_output.$mainCard.$mainProfile.monitor" ]]
then notify-send -t 500 "Main sound output on!"
elif [[ $(pactl get-default-source) == "alsa_output.$altCard.$altProfile.monitor" ]]
then notify-send -t 500 "Alt sound output on!"
else notify-send -t 2000 "Something weird happened."
fi

# Optional audio notification. It runs VLC but it's easy to adapt or remove if you want.
cvlc --play-and-exit /usr/share/sounds/freedesktop/stereo/message-new-instant.oga

Check the first four lines of code. You'll need to replace that "pci.blahblah" and "audio.stereo.whatever" junk with the ones from your machine. To know them, run pacmd list-sources | grep name: in a terminal. The output will look like this:

name: ⟨alsa_output.pci-0000_06_00.1.hdmi-stereo-extra1.monitor⟩
name: ⟨alsa_output.pci-0000_00_09.2.analog-stereo.monitor⟩

Ignore ⟨alsa_output and monitor⟩. The second-to-last chunk (e.g. hdmi-stereo-extra1) is the profile. The rest (e.g. pci-0000_06_00.1) is the card. Now replace those in the script.

*credits: this script is partially inspired on this AskUbuntu comment.