After the controller and app have connected to the Phantom, if I walk around with the drone and controller the DJI GO app says something that sounds like "addy mode" but I can't quite decipher what it is saying... does anyone know what it is trying to say?

Hi and welcome. l'm guessing this is your first Phantom, and l woud highly recommend reading the manual thoroughly (it can be downloaded from the DJI website) and watching some videos on the workings of the drone before flying.

The app is saying "Atti mode" meaning the drone has flipped from GPS into Atti mode. lf you put your hand on top of the drone to turn off the battery before the transmitter (which you should always do) you will hear the app say it then, or any time it loses GPS/VPS.
The tiny switch at the top=left of the controller says PAF  - P is for P-GPS (normal flight mode).  A for atti mode (using only the barometer for holding position, will drift in wind). F is the IOC, intelligent orientation control, directions are in manual.

It is saying Atti mode,  which means flight mode switch  is in A



mode which means no gps.  
It's all in the manual.

yes no satellite link up attitude mode. For advanced flyers. As suggested I would read all the manuals and watch all the tutorials. The Phantom 3 is a very grown up toy ;) and needs to be fully understood and flown responsibly.

Thank you everyone for the responses! It makes sense now.