There is an almost 3.5 year old issue with Yealink T4xG series phones and the LE cert generated by FreePBX. If you, instead, generate a cert manually with certbot and import it, it works perfectly.
No one from Sangoma has chosen to do anything about it, and it was beyond my skill to troubleshoot.
Original thread: Yealink T4XG phones will not autoprovision over HTTPS with FreePBX 14
Issue made later: [FREEPBX-21011] LE Cert does not work with various Yealink phones - Sangoma Issue Tracker