Sounds like you have Thunderbird configured as POP on your computer. POP only knows about the Inbox on the server. It saves all messages sent from the computer locally and does not see the Sent folder on the server where your phone is placing them.. You need to use IMAP to sync all folders on the server with all your devices. I suggest you Google IMAP vs POP so you understand how the two protocols work and differ. Mainly if you delete a message from the server or any device is is gone everywhere. That seems to surprise many people. This article tells you how to switch your account settings in Thunderbird from POP to IMAP. '''Do NOT try to change the existing account in Thunderbird.''' https://support.mozilla.org/en-US/kb/switch-pop-imap-account