I got Chromecast "working" from my Sony Xperia XZ Premium phone to my Sony KD-65X9300D Android TV just for fun. Both devices have Chromecast built-in.
That required the TV to be rebooted just to get started. Not encouraging.
Anyway, casting an MKV movie from Gizmo on the phone to the TV was extremely unreliable. I thought it was just stopping for others at the beginning of the movie, but it keeps happening through the movie even if you can restart it after it stops. I restarted by dragging the position slider a little. Pause and Play didn't restart it.
You can see what is going on in the "Services & Plug-ins > Media Network" function. I didn't try to solve the problems though. I did try with BubbleUPnP and saw the same issues, so it is probably a Chromecast or Android issue.
The good news is that screen mirroring from the phone to the TV worked fine, and the movie played without pause, after a very brief mini pause at the beginning. The phone turned its screen off, which is a setting in the phone, so didn't flatten the battery as fast,
So do your phone and TV support screen mirroring? If so, use that.