No, you can't. You can be logged in to the mobile app and the desktop client at the same time, but you can't receive calls on both devices. So, if there's an incoming call, you can't choose which device you want to answer the call on.

If you're logged in to mobile app and the desktop client at the same time, you choose on which device you want to receive calls.

Thanks to the little switch, in the lower left corner in the desktop client, you see if you're online for Calls, and on which device.

Online and will receive calls in the desktop client:

Online and will receive calls in the mobile app:

Also in the mobile app, you can see if you're online on the phone and on which device you're online.

Online and will receive calls in the desktop client:

Online and will receive calls in the mobile app:

Read more about how to go online on the phone and join the queues in the mobile app here: How do I go Online to receive calls?