I have only ever had this issue with wired heaphones/speakers.
Quite annoyingly, it will often open up Google Assistant, which I detest in the worst way.
As for wired devices, I think it is caused by a bad/dirty connection between the phone jack and the plug, and/or the plug and the cord.
The phones/speaker may even work perfectly fine when connected to other equipment.
So to me, this means that even a change in impedence could cause this.
However, none of this would be involved with wireless phones/speakers.
Now, I have recently obtained yet another bluetooth speaker.
Each one I get seems to be quirky in its own right.
This one, which also has a built in mic so that I can use it for calls, somehow triggers the device to jack the volume to the maximum (in about two brief steps) during a call, and I don't believe that the volume returns to normal when the call is disengaged.
Sorry, the speaker is pretty small, so it really isn't much of an issue- so I haven't paid close enough attention to have noticed.
Quite possibly, there is a volume control on your phones/speaker (almost assuradly on the speaker(s)).
So what to do if the speaker has volume control?
Leave the volume on your phone all the way up. It seems to like this anyway, right?
Control the volume from from the speaker.
Without going into more blah, blah, blah, etc. as to why, there is a volume that a speaker can handle constantly- indefinitely if you will- and that is approximately 71% of its total volume.
On an Android phone with 15 volume steps (typical in my experience) this is close to 10 volume steps from 0.
As long as you remain at or below this amount at the speaker's end, you should not damage anything.
And yes, techically you can inverse this, by having the speaker volume at 100% and not going past 71% on your phone.
But your phones have not been consistant, so as inconvenient as it may be, controlling the volume at the speaker may be the best solution.
And, because of there being 15 steps of volume, the numbers don't quite work out to that golden 71%.
It is a user's choice between 67% and 73%.
Generally I find that 67% is just right to a bit too soft, and 73% is just right to a bit too loud.
Fun, right?
Anyway, the Androids that I have dealt with do not hurt themselves when played at full blast- unless you use sound enhancing apps- like equalizers, bass boosters, volume boosters, etc. and overdrive the internals.
You will hear distortion at that point.
Distortion is always bad in this case.
Android does a pretty good job of preventing overdriving itself like this, but it still can happen.
This can actually damage internal audio parts.
This is why sometimes when you use an EQ to boost some frequencies the total volume actually seems to decrease. This is Android protecting itself.
And digital music is not much help either, as it seems that almost every song is recorded at a different level.
Of course, the loudest one in your library will play right before the quietest one, or vice-versa.
Is it on purpose?
Only God knows, but it is fun to speculate, lol.
P.S.
On two of my bluetooth speakers, the 'skip ahead/back' buttons raise and lower the speaker volume when pushed in and held.
