Split View, which is actually available on iPad Pro, is only
part of multitasking. That being said, all iOS devices have some level of multitasking.
Regarding Split View, the functionality is built into iOS but Apple has made a decision to not propagate it over to iPhone. I'm by no means an Apple apologist but I don't blame them for not offering it on iPhone. Most people I know who have it available on their Android devices don't use it because squeezing an app into an already small display kills the user experience.
https://support.apple.com/en-us/HT202070