This is just my guess since no one yet has responded.
A few questions come to mind (Sorry, I know, I hate asking question with questions):
Does every call gets dropped prematurely? Was there a recent phone software update/upgrade prior to the drop-call issue occured? Do you have another Bluetooth device in the car at the time that may be interfering?
Personally, I would completly delete the phone then establish connection between your cell phone and the vehicle audio/Entune system...
Ah! There have been a couple of threads with people talking about similar issues, one of which is titled "Bluetooth Issues" if I recall correctly and a couple more even before that. Ultimately, they upgraded their phones to iOS 13.2.2 with issue resolved. Hope for you as well.