To determine which species is most closely related to species 4 based on a phylogenetic tree, you would generally look for the species that shares the most recent common ancestor with species 4.
Since I don't have access to the actual phylogeny (the tree itself), I can't make a definitive conclusion about which species species 4 is closest to. However, if you see that species 4 and species 3 share a more recent common ancestor than species 4 does with species 1 or species 5, then you would choose 3. Conversely, if species 1 shares a more recent common ancestor with species 4, then you would choose 1.
If the common ancestors are equidistant or if it's unclear based on the tree, then the answer would be "1 or 3 (Can't tell)".
If you have information from the tree, please share, and I can help narrow it down!