@askdannyb ,
What I could suggest it for you to use Zoom Desktop Application if ever you will be joining meeting and use your Zoom mobile app if in case you will be accepting phone calls. As long as you use two separate applications you should be able to join both at the same time but using different Zoom application instances (mobile and desktop app).
Have any of these answered your question? If so, don’t forget to mark the reply as an accepted solution.