To accurately determine which species is most closely related to species 4 based on the phylogeny, we need to examine the tree structure that illustrates the evolutionary relationships among the species. Typically, species that share a more recent common ancestor are considered more closely related.
Since I don't have access to the specific phylogeny you're referencing, I can't definitively say which species is most closely related to species 4. If species 4 shares a more recent branching point with species 3 than with species 1 or species 5 in the phylogeny, then species 3 would be the closest relative. Conversely, if it shares a more recent common ancestor with species 1, then species 1 would be closer.
If you're unsure or the phylogeny is ambiguous in regards to the relationships, the answer could be "1 or 3" (as you mentioned).
Please refer to the specific phylogenetic tree to make the most accurate determination. If you have details about the tree structure, feel free to share, and I can help analyze it!