What is the ruling on congratulating people on the advent of the month of Ramadan with the phrase: "May you be well every year (Kul 'am wa anta bi-khair)"?

There is no specific wording for congratulating someone on the advent of Ramadan. It is permissible to congratulate using any common phrase such as "May you be well every year" (كل عام وأنتم بخير), provided it does not contain anything forbidden by Sharia.