You need to have essential license to cover the analogue devices.
My question is can we create a generic user account and assign to the phones to free up licensing >>> Do you have any free license available ? Lower tier will borrow from upper tier if license available. What you expect by assigning users.
Could you share the license usage screenshot from PLM/ELM or smart account.
Since you are in Lock state, contact Cisco licensing TAC/Local Cisco SE for a demo license and Fix the license compliance and Then you can make changes.
Few days back my customer had a similar issue , His call manger has crossed grace period to fix the license issues. But when he restarted the CUCM he got another one more day and he could fix the license problems. The CUCm version was 10.5