I got mine working by adding credit/debt card info in addition to phone verification, however when I was struggling with it I attempted to use ODH, only to find it it only works via Bluetooth, and I don't have a computer with Bluetooth capabilities. As in IT Manager, I hardwire everything, so it doesn't make since for me to buy wifi/bluetooth modules for all of my PCs. Surely I'm not the only one.
Update 11/8: The fix pushed to the latest App Update does not seem to have fixed the issue for all developers. At this time we are re-opening the issue and will update this forum thread with any relevant details: https://forums.oculusvr.com/t5/General-Development/Developer-Mode-Issues-Update/td-p/892227
In the meantime, many of our awesome developers have shared that verifying using a Credit Card allowed the Developer Mode option to appear.
Update 11/15: We have received reports that this issue has been fixed for most developers experiencing this issue. Please log out and log back into your Oculus app and try enabling Developer Mode once more. If you still experience the same issue, please reach out to our team at https://developer.oculus.com/support (click "Contact Us") and we'll dive deeper.