A trival Emacs package that defines an input method for entering Unicode math characters using LaTeX macros.
Most of the work is done by math-symbol-lists, which defines the tables.
(set-input-method "unicode-math-input")or you can invoke set-input-method using C-x RET C-\.
Then typing \rho \equiv \alpha + \phi would enter ρ ≡ α + ϕ, etc.
See the variable math-symbol-list-basic.