His voice was garbled during the video call because of poor internet connection.

garbled 是动词 garble 的过去分词形式，garble 的意思是"混淆、使混乱"，通常指声音或信息因干扰而变得难以理解。garbled 在这里描述的是声音因网络问题而变得断断续续、不清晰的状态。