While all Bluetooth speakers can play music from your Android phone,
not all of them can do phone calls from your Android phone. And it sounds the particular Bluetooth speaker you've got in the house is one that doesn't do phone calls, and is music only.
This "S01" speaker can't do phone calls from my Android phone...
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...while this "S20" speaker can do phone calls from my Android phone...
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One has Phone Audio support while the other does not.
There's two separate Bluetooth profiles here. HeadSet Profile (HSP), which is used for phone calls and is mono, and the Advanced Audio Distribution Profile (A2DP) which is used for music etc, and is high quality stereo. And not all Bluetooth speakers support the former (HSP) one.
You'd need to check the speaker manufacturer's instructions and specs for this.