Webpack 4, how to import a module into another module that are both entry points?

I'm new to Webpack, so my terms may not be entirely correct. What I'm trying to do is build a custom Phaser module first, then import it into the other entry point, which depends on it.

EDIT: I've tried using SplitChunks, Dynamic Imports, and aliases. But no avail. Is there anyway to accomplish this via plugins or methodology?

From webpack.config.js:

entry: {
       'phaser.min': './phaser-builder.js',
       game: './src/index.js'

   },

   resolve: {
       alias: {
           'eventemitter3': path.resolve(__dirname, './node_modules/eventemitter3')
       },
       modules: [ 'node_modules/phaser/src', 'node_modules' ]
   },

   output: {
       path: path.resolve(__dirname, 'build'),
       filename: '[name].js',
       library: 'Phaser',
       libraryTarget: 'umd',
       sourceMapFilename: '[file].map',
       devtoolModuleFilenameTemplate: 'webpack:///[resource-path]',
       devtoolFallbackModuleFilenameTemplate: 'webpack:///[resource-path]?[hash]',
       umdNamedDefine: true
   },

Contents of phaser-builder.js:

require('polyfills');

var CONST = require('const');
var Extend = require('utils/object/Extend');

var Phaser = {

   ... code ...
};

Phaser = Extend(false, Phaser, CONST);
module.exports = Phaser;
global.Phaser = Phaser;

index.js (second entry point) needs the 'Phaser' object from phaser.min.js that is created from ./phaser-builder.js (first entry point) as shown below:

Contents of index.js:

//import 'phaser';  //this works but it's not the custom build from entry point one.
import { Phaser } from '../build/phaser.min';
import { TestScene } from './scenes/TestScene';

const gameConfig = {
  width: 680,
  height: 400,
  scene: TestScene
};

new Phaser.Game(gameConfig);

Contents of TestScene.js: (imported in index.js)

export class TestScene extends Phaser.Scene {
    preload() {
    this.load.image('logo', 'assets/sprites/logo.png');
    }

    create() {
        this.add.text(100, 100, 'Working...', { fill: '#0f0' });
        this.add.image(100, 200, 'logo');
    }
}

As commented in index.js above, if I simply use import 'phaser'; (which is pulling from node_modules I presume?) Everything works fine. But that is the full phaser lib, which I don't want. I want to import the custom build I created in entry point one, that exists in /build/phaser.min.js

If I try importing from /build/phaser.min.js I get this error:

"TypeError: Super expression must either be null or a function"

Which from my understanding is basically saying that Phaser object/module is undefined, so TestScene is not extending Phaser.Scene as expected.