Get a digital aneometer if you are worried. Here's some guidelines. Lets say your phantoms top speed is 30mph, you wont want to fly in those wind speeds but winds can gust and a steady 20mph wind can easily gust over 30mph with no notice. Now thats at ground level. Winds aloft, or up higher wind speeds can increase significantly. 15mph wind speed on the ground could easily be over 30mph a few hundred feet up in the air. My rule generally is 15mph on the ground means I keep under 200ft, 20mph and i'll stay lower. I dont strictly stay to these rules but if its windy I'll keep an extra eye on my bird and be wary of the wind. Dont fly out of line of sight when windy and fly into the wind if you must, at least that way she can only blow back to you rather than VERY quickly away from you. Experience will help you.