I use all cast. It cost a few bucks, but it works flawlessly (and I had problems with the alternatives). It can stream to Android TV and Chromecast (obviously), Apple TV, and I think fire stick, Xbox, etc. It also works perfectly with showbox.
If casting via one of the already-mentioned apps is a no-go, then you could install an app which exposes your phone's filesystem as a network share and add that as a source within KODI. Can't remember the app I used, it was a kind of one-for-all which had loads of different types of servers you could start and stop on your phone. Might have been this one .
Providing you're on the same network that should work just fine.
The best way to play content from your phone would be casting it.
Is there a reason you rather not, or looking for another way? Maybe if it is something specific, we can think of a work around. Like if it is a storage issue than maybe use a USB drive or cloud/NAS.