iOS is restrictive. Your only option is a web-based emulator like (search on GitHub) or using AltStore to sideload a modified version of J2ME Loader. This requires developer mode.
Before diving into the download links, it is crucial to understand resolution. Java feature phones (Nokia, Sony Ericsson, Samsung, LG) came in dozens of screen sizes. The most common were 128x160, 176x208, and 240x320.