Personally I don't thing there is anything wrong with being aware of someone watching what you are doing on your phone in a crowded public place. There always seem to be some nosy people who try to see what everyone is doing. That is why I refrain from using my phone in public unless I have to. In my experience though, as far as withdrawing from social situations, I think it makes it harder to get back into it after awhile. Continually putting yourself into social situations will eventually make you used to it, as long as you don't put yourself in extremely difficult situations, like huge crowds. The more you socialize, the more natural it becomes and the easier it gets.
Take your therapists advice,it seems like she knows what shes talking about.