There is no such thing as a Thunderbird account. Thunderbird is client software running on your computer. Are you using IMAP format for your email on both the computer and the phone. Since Thunderbird does not run on phones you may need to ask your phone vendor for help with this.

When I first established Thunderbird as my email "client software" I received all my emails on both my android phone and my computer. A while ago I stopped receiving many of my emails on my android phone that I did receive on my computer. My "account" settings are still designated a POP instead of IMAP. Do I re-establish new account settings in Thunderbird or will it do it automatically. I have always updated and I have the latest version.

Do you have Thunderbird set to leave messages on the server? The default operation for POP is to download the messages to the device and remove from the server. Then they are not available to other devices. IMAP is server based and you view messages remotely from your devices. It is designed for checking messages from multiple devices.