Please note that I do not own an iOS device. What I am posting here is gleaned from other posts in the FM Go forum and here. Test the ideas carefully and, if needed, post any follow up questions in the FM Go forum. (See tabs at top of this screen.)
Best way is to link FM Go on the iPhone to a database open and hosted on your desktop computer.
If you can get a good connection via wiFi, 3g or (using FM Go 12) 4g, your iPhone can simply function as a client of the hosted database on your desktop.
If you don't have that option available, you can create two files. File 1 is hosted on your database. File 2 is installed on th iPhone, but contains external data source references to the tables in File 1. To move data from your iPhone to your desktop machine, you can then gather your data independently in tables local to your iPhone, but then return WiFi range of your desktop system, connect to it and then Import records from File 2 on your iPhone can import data into File 1's tables by using Import Records and specifying the table occurrences that have remote data source links to tables in File1. The imports can be scripted.