You’ll fall in live with your harmony - maybe he means, again since in YOI music is to portrait feelings, he means that Yuuri will find harmony somewhere and finally get his skating better?
And that, he’ll love his new found himself? Phichit means self-love, he knew Yuuri was anxious type.
You can stand like a feather on the ice. He means how otherwise clumsy Yuuri is like a feather on ice, his whole body in balance and harmony.