Bluetooth connectivity

I've owned my Karoq Edition since 2018 and have owned three different mobile phones in that time.

My first phone connected with the infotainment (Columbus) system without issue and all calls were via the car.

My other two phones however are patchy at best and I don't know if this is down to settings within each phone or the the car.

Sometimes calls are connected through the Columbus via bluetooth but this only happens about 50% of the time. The rest of the time the phone can be answered/connect using the car system however, the phone doesn't automatically feed the audio via the car and you have to access the phone settings and select which bluetooth connection you require.

I don't understand why I don't get the car being the default option every time I need to make or receive calls whilst driving.

Any ideas?