Xtreix There are no phones with open-source firmware to my knowledge.
It would be great if there were, but that is not the state of affairs.
For a while the GNU fork of Android, called "Replicant", sort-of ran on some phones, though many "supported" models couldn't do Wi-Fi, or couldn't do Bluetooth, etc., because there was no open-source firmware for those functions.
Here is a recent status update from Replicant: https://blog.replicant.us/2024/03/replicant-status-and-report-of-the-37c3-and-fosdem-2024-conferences/
Perhaps their approach will eventually bear fruit (that would be great), but at present it's not really resulting in usable phones.