Consonant cluster simplification is a widely observed phonetic phenomenon among learners of English as a Second Language (ESL), particularly those whose first languages (L1s) restrict complex consonant sequences. This study investigates the patterns, types, and phonetic motivations behind consonant cluster simplification in ESL learners. The primary objective is to analyze how ESL learners modify English consonant clusters in onset and coda positions and to identify the influence of L1 phonotactic constraints on these simplification strategies. Using an acoustic and auditory phonetic approach, speech data were collected from ESL learners through controlled word-list reading and spontaneous speech tasks. The findings reveal that learners frequently employ simplification strategies such as consonant deletion, vowel epenthesis, and cluster reduction, especially in word-final and tri-consonantal clusters. These patterns are largely attributable to L1 transfer effects, articulatory difficulty, and limited exposure to native-like pronunciation norms. The study also demonstrates that proficiency level plays a significant role, with advanced learners exhibiting fewer simplification processes than intermediate learners. By highlighting systematic phonetic patterns in learner speech, this research contributes to the broader field of second language phonetics and provides pedagogical implications for pronunciation teaching. The findings emphasize the importance of explicit phonetic instruction and targeted pronunciation training to help ESL learners overcome persistent difficulties related to consonant cluster production.