Could you take a look at the Using Thunderbird with Google Calendar support article in case you haven’t yet?

That provides some help, but not enough. I don't want to use Google calendar, but apparently I have to use it as a go -between in order to sync Thunderbird's calendar with the one on my phone. I don't know whether I need read only or read/write, for instance. So how do I set that up?

gyaltnnh said

How do I sync calendar with google calendar?

Both devices need to sync to a common calendar. That generally means one that they can both access. So you need a server to run and expose the calendar for you. If you have an Android phone then Google Calendar is the path of least resistance.

If you have the use of an ftp server, or some similar service such as Dropbox then maybe you could approximate synchronisation by storing the calendar in an ics file, and have each device access it.

Or if you have the use of a calendar operated by your email provider or ISP, perhaps using CalDAV, maybe that would work.

But I haven't yet managed to make the calendar app on an Android device work with ics or CalDAV.

I'm just a Thunderbird user, not a computer wiz or networking expert, but I do understand that in order to synchronize the calendar function that's been built into Thunderbird with another calendar app on my phone, I need an intermediary on a server someplace in the cloud. Google calendar appears to be the best option, but does that mean that I have to see and use google's calendar in place of the built-in function in Thunderbird? If not, then how do I set up the sync? I do not find anything within the tools or options in Thunderbird to get me started.

You add the synchronised calendar to Lightning. File|New Calendar|On the network.

The easiest way to do this is to install the Provider for Google Calendar addon. There is also built in support for CalDAV which both Lightning and Google Calendar can use but it is not so easy to set up.

I really don't think I've said anything here about using Provider that wasn't covered in the link provided earlier.