The need to connect with learners is essential to successfully transfer learning. Thus, the medium of instruction plays a very important role. One indicator that would tell us if success is attained in teaching various subject areas is also influenced by the medium of instruction which is employed in the classroom. It is on this premise that the researcher wanted to examine the efficacy beliefs of teachers of subjects other than English in various faculties in the Philippines in terms of their perceived English language proficiency level and their use of English as a medium of instruction. Global English's adapted form of Business English Proficiency Level Scale was used to validate the competency level across various scopes including, English language familiarity, language application on various fields or disciplines, usage of communication skills in various contexts, such as in demonstration, discussion, conference, meeting, etc., In-depth analysis and understanding of complexity and nuances in different teaching related circumstances and the capability to substantially contribute in discourse related to teaching-related investigations, problems, and resolutions. It is evident in the results that the self-reported English proficiency was positively correlated with the perceived efficacy of the respondents. The findings also showed that for the respondents to appear proficient in using communicative based strategies, the respondents had to exude more confidence in using English as a mode of instruction.