hey man.
Stop making excuses
If a girl is talking on the phone, its rude to interupt, but you can wait till she finnishes the call then make your approach.
If she is txting, she cant possibly be txting for more than 30 seconds or so, wait till shes finnished if you want, or just approach.
If she is just on her laptop, or reading a book, or doing whatever.. interupt! So long as you are polite, its not an issue!
Deal with it by recognising its really not a problem. Most people are doing
somthing all the time, and generally speaking, you can interupt them so long as you do it right.
Good luck
Cure.