Voice calls given priority over VoIP calls on iPhone

[colinuk]

When on a 3CX call on an iPhone, if I receive a mobile call, the incoming call takes precedence and puts the other call 'on hold' in the background - the caller has no idea I am not talking to them - when the call is finished - the original resumes
No warning or option given.
I found the following explanation on an older thread - is there any update or option to control this now - understanding it is probably an iPhone setup/ control issue:
I am using an iPhone 11
https://www.3cx.com/blog/docs/voip-call-vs-gsm-call/

 

[Vali_3CX]

Can you provide a short screen video recording? Upload it on dropbox or something similar and provide the link (either here, or me by PM if contains sensitive data).

When a CallKit call (in our case 3CX) is interrupted by another incoming CallKit call (say GSM, FaceTime, Whatsapp etc) it's the CallKit who manages these calls, including putting the current one on hold, according to what USER decides to do (decline, hold and accept, end and accept)