Yes, long range (Coded PHY) is supported in Zephyr 1.14.0. However, Bluetooth Mesh builds on BLE 4.2 as of now, which does not support long range, so you won't be able to use coded PHY alongside Mesh. You could take a look at this case, which modifies the radio mode with mesh, although I don't how easy this would be to implement in Zephyr.
