I set up my new Andriod phone email app with my Thunderbird account.

There is no such thing as a "Thunderbird account". You've set up an account with an email provider, e.g. Gmail or Yahoo. Then you use Thunderbird to access mail for that account on your email provider's server, and to send mail via your email provider's server.

Android email app on phone connected to Thunderbird now sends emails with no body text

I'm not sure whether you have problems when sending from the phone or from Thunderbird. I'm assuming the latter. For problems with your phone please contact the email app vendor you're using on the phone.

my contacts are letting me know that my emails have no body text, just the subject.

This is not necessarily a problem at your end.

When I go to my Sent box, I can see the body text in the preview, but when I open it, the body is blank.

Technically there is no message preview. I'd assume with preview you mean when a message is selected in the thread pane and the actual message shows up in the message pane. This is equivalent to opening the message in a new window or tab. Are you saying you do see the message content in the message pane, but you don't see it in a new window?

You can try to copy a message showing that behavior to another folder. Right-click the message in the thread pane - Copy To

Is there any difference?

So far, you are correct that I am not using the right language to convey what is happening. I mostly do not possess the language - but from you replies, I do know that it is not a Thunderbird problem, and I will go form here. Thank you for your time.