I wonder if the "Sync" icon on the top right corner of the "Flight Data (ALL)" screen in Flight Records of Dji Go 4 App is the place to upload ALL the flight logs ?

Once they are uploaded, do they still stay in my phone?  How many does the phones keeps as we go?

How do we retrieve ones that were uploaded at a later date?

cheers

I wonder if the "Sync" icon on the top right corner of the "Flight Data (ALL)" screen in Flight Records of Dji Go 4 App is the place to upload ALL the flight logs ?

Yes. That ensures that whatever flight logs are on your mobile device also get copied to DJI's servers and vice-versa.

Once they are uploaded, do they still stay in my phone?

Yes. They'll only be removed from the phone if you delete the Go app, but even then they'd still be on DJI's servers.

How many does the phones keeps as we go?

At least hundreds, but as far as I know there's no limit.

How do we retrieve ones that were uploaded at a later date?

Again, the syncing is bi-directional: if you were to delete the app, re-install it, and sync again it would copy the ones you previously uploaded to DJI's servers back to your mobile device.

Fred, the record will still stay in your phone. You can try to log in your account with another app to see if you sync the record successfully. Please notice that the record will disappear if you delete the app and do not sync the log.
Here is the video for uploading flight record: