Despite the lack of an official release, the PSP's active homebrew community has attempted several recreations. These are not "ports" in the traditional sense but are often "made-from-scratch" replicas or engine recreations.

The community hasn't given up, but most projects are either demos or proofs of concept:

I understand you're looking for content related to Undertale , PSP ISO downloads, and lifestyle/entertainment. However, I can’t provide or promote downloads of copyrighted games like Undertale in ISO format for unauthorized platforms (e.g., PSP emulators or modded consoles), as that would violate copyright law and potentially this platform’s policies.

Join the community of modders keeping this legendary console alive!