Hello,
The reason I am asking is that I crashed and lost my drone off coast of California.

When i use the "locate my drone".
it shows me an incorrect location,
and it kept showing different locations even when I reboot the app.

I know that the phone I am using had issues with GPS locations in the past,
cause it kept bumping me everwhere whenever I use car navigation and pokemon go.
Which is why i had to get a new phone for personal use, and this old would be dedicated for the drone.

Thanks.

I am sorry that your drone crashed. Let me help you with this issue. May I know what is the model of the mobile device that you are using?

You could upload log to link below it might help.
Just click on link and follow instructions come back here and post your link

http://www.phantomhelp.com/LogViewer/Upload/

I'm not really sure what happened with your device, but to answer your question,  No.  your device does not need to have any connection.  The device I use has no service, WiFi is turned off, and is also in Airplane mode. and i don't have issues.

EDIT:  As I was reading, I did some checking and found that airplane mode does not disable GPS, so my statement above holds no weight.  I don't actually know if GPS on my phone is being used or if it is the aircraft.  I'll try to find more answers to give a more definitive answer.