What do you expect to achieve by doing this? What is it that you want to synchronise?

The usual way to synchronise is to use a common resource that both of your devices can connect to. So they both synchronise to that resource and so are effectively synchronised to one another.

That means using IMAP for email, and services such as Google Contacts for your address book, and Google Calendar for your diary. It doesn't matter exactly what client you use so long as they all connect to the same server.

I mention these two Google services in particular because you tell us it's an Android phone, and so comes pretty well automatically connected to these services. So what remains is to use the appropriate addons in Thunderbird to allow it to connect. Provider for Google Calendar allows Lightning to use a Google calendar, and gContactSync lets you connect Thunderbird's address book to Google Contacts.

Zenos, thank you very much. I guess I have not given enough thought to the syncing process. I assumed (I know, I know) it consisted of both devices talking to each other to determine what was common between them. Using a third device (in this case Dropbox) to be the recipient of the latest changes in this 'database' removes that responsibility from both of the inputting devices.

Once again, I thank you for the education.