I can understand what you are saying, it's not jumbled to me. I'm not sure why, but it seems as though the phone just doesn't like calls with a wired speaker connection? Maybe it's trying to pass call audio through the headphone jack? I'm not even sure if that is possible? If I think of it (and can find an aux cord) I will try a call using that setup with my phone. Depending on what you plan on spending on a BT headset, you might want to consider a car kit like this one.
https://www.amazon.com/gp/product/B00GJFGE0K/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
I use it in my Jeep, and another in my daughter's older model Nissan. I drive a Jeep Wrangler every day, and they are not known for being super quiet. I have no problems with calls, as long as I talk loud & clear (which I always do, side affect from my former career

). With this I am completely cable free from my phone to the receiver, and can listen to music, make calls, Google Now commands, listen to texts, etc all over the Bluetooth connection. The music quality is very good, in my opinion. $30 is not super cheap, but you might spend the same, or more, on a good BT headset. Just an idea.