Hi Eva,
you are allowed to do that during the preliminary phase. There is a guided procedure, during which you will get a code on your phone that will allow to take pictures and associate them to your check-in procedure on you computer. In order to get familiar with this procedure, I'd recommend to run a system test at this link:
home.pearsonvue.com/pmi/onvue
. This is very similar to the one you will run on the day of your online exam; it's just a shorter version.
As soon as I completed this phase, submitting pictures of the workspace and ID, I put my phone off and stored in a drawer not accessible from my desk.
Hope this helps,
Gabriella