when I play a note on my piano, the iGrand sound (Yamaha grand with violins) comes out of my phone as oppose to the piano.
I was told that the Kawai ES110 doesn't have audio input - it only sends data out. I was shocked to hear that. I used to have a Roland FP4 that let me use iGrand, and it was in a similar price range.
Even on the FP4, you'd have to run a separate audio cable out of the phone and into the piano's aux inputs. But yeah, the ES110 does not have those jacks. The ES110 is better than the FP4 in some ways (piano sound, travel weight, possibly action), not as good in others (connectivity, speaker volume, range of additional sounds, operational ergonomics). Though IIRC, the FP4 typically healthily topped $1k. The "current version" of the FP4 is the FP50 at $1299.
Kawai isn't alone in not offering audio inputs on their entry level board... you similarly won't find them on the Yamaha P45/P115, Casio PX160, Roland FP30.
(As an aside, I don't think anything has real-time bluetooth audio, audio over bluetooth tends to have too much latency. There are a handful of workstation-style boards that can take audio in over USB, though I don't think I've seen that in any models with speakers.)