Antonyms for the phrase "becoming lenient" would include words like strict, inflexible, unbending, rigid, firm, and unyielding. These terms describe a person or situation that is not willing to bend or compromise when it comes to rules, standards, or expectations. In contrast, becoming lenient means to loosen up or relax these same rules or standards. While there may be times when leniency is appropriate or even necessary, there are also occasions when being strict is important. It's all about finding the right balance between being firm and flexible and knowing when to apply which approach.