It says "Mode changed to GPS_Atti" right before you initiate an auto takeoff. It looks like you had signal but manually changed the controller switch to atti mode. I don't know for sure but I think GPS_Atti is when you switch to Atti mode but have GPS signal, then Atti mode is when you have no gps signal and the Phantom switches into this mode automatically when you lose GPS connection. You didn't lose GPS connection, you switched into Atti mode. In Atti mode GPS is not used for stabilization but it can still return to home if you have satellite connection. Also in atti mode the Phantom does not use air brakes so after you stop it will drift in the direction it was traveling until you correct it yourself. It is a good idea to practice flying it atti mode higher than any obstacles so you can see how it drifts and what you need to do to correct it when it does drift.
